Multi-spectral radio-frequency localization techniques and associated systems, devices and methods

ABSTRACT

A device comprising: a receive antenna configured to receive a first radio-frequency (RF) signal having a first center frequency; a first transmit antenna configured to transmit a second RF signal having a second center frequency that is a harmonic of the first center frequency; a second transmit antenna configured to transmit a third RF signal having a third center frequency that is a harmonic of the first center frequency and is different from the second center frequency; first circuitry, coupled to the receive antenna and to the first transmit antenna, configured to generate the second RF signal using the first RF signal and provide it to the first transmit antenna for transmission; and second circuitry, coupled to the receive antenna and to the second transmit antenna, configured to generate the third RF signal using the first RF signal and provide it to the second transmit antenna for transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119 to U.S.Provisional Application Ser. No. 62/268,741, titled “FREQUENCY-SHIFTTRANSPONDER,” filed on Dec. 17, 2015; U.S. Provisional Application Ser.No. 62/268,745, titled “RADAR ON A CHIP,” filed on Dec. 17, 2015; U.S.Provisional Application Ser. No. 62/275,400, titled “HIGH-PRECISIONPOSITIONING SYSTEM FOR A GROUND PENETRATING RADAR SYSTEM,” filed on Jan.6, 2016; U.S. Provisional Application Ser. No. 62/306,469, titled“HIGH-PRECISION TIME OF FLIGHT MEASUREMENT SYSTEM FOR PICKING ANDPACKING,” filed on Mar. 10, 2016; U.S. Provisional Application Ser. No.62/306,478, titled “HIGH-PRECISION TIME OF FLIGHT MEASUREMENT SYSTEM FORMICRONAVIGATION AND LOCALIZATION,” filed on Mar. 10, 2016; and U.S.Provisional Application Ser. No. 62/306,483, titled “HIGH-PRECISION TIMEOF FLIGHT MEASUREMENT SYSTEM ON A CHIP,” filed on Mar. 10, 2016, each ofwhich is incorporated by reference herein.

BACKGROUND

The ability to accurately determine the location of an object or targethas potential benefits for numerous applications. Some exemplaryapplications benefiting from object localization include motiontracking, virtual reality, gaming, autonomous systems, robotics, etc. Anumber of technologies have been pursued that seek to providelocalization, including global positioning system (GPS) technology,received signal strength indicator (RSSI) measurements, optical imagedata processing techniques, infrared ranging, etc. Generally, theseconventional approaches are limited in application due to one or moredeficiencies, including relatively poor or insufficient accuracy and/orprecision, computational complexity resulting in relatively long refreshrates, environmental limitations (e.g., operation limited to outdoors,cellular or network access requirements and/or vulnerability tobackground clutter or noise), cost, size, etc.

SUMMARY

Some embodiments provide for a system comprising: a first interrogatordevice, comprising: a first antenna configured to transmit, to a targetdevice, a first radio-frequency (RF) signal having a first centerfrequency; a second antenna configured to receive, from the targetdevice, a second RF signal having a second center frequency that is aharmonic of the first frequency; and first circuitry configured toobtain, using the first RF signal and the second RF signal, a firstmixed RF signal indicative of a first distance between the firstinterrogator and the target device; a second interrogator device,comprising: a third antenna configured to transmit, to the targetdevice, a third RF signal having the first center frequency; a fourthantenna configured to receive, from the target device, a fourth RFsignal having the second center frequency; and second circuitryconfigured to obtain, using the third RF signal and the fourth RFsignal, a second mixed RF signal indicative of a second distance betweenthe second interrogator and the target device; and at least oneprocessor configured to: determine the first distance based on the firstmixed RF signal; determine the second distance based on the second mixedRF signal; and determine a location of the target device using thedetermined first distance and second distance.

Some embodiments provide for a system comprising a first interrogatordevice and a second interrogator device. The first interrogator devicescomprises: a first antenna; configured to transmit, to a target device,a first microwave radio-frequency (RF) signal having a first centerfrequency; a second antenna configured to receive, from the targetdevice, a second microwave RF signal having a second center frequencythat is a harmonic of the first frequency; and first circuitryconfigured to obtain, using the first RF signal and the second RFsignal, a first mixed RF signal indicative of a first distance betweenthe first interrogator and the target device. The second interrogatordevice comprises: a third antenna configured to transmit, to the targetdevice, a third microwave RF signal having the first center frequency; afourth antenna configured to receive, from the target device, a fourthmicrowave RF signal having the second center frequency; and secondcircuitry configured to obtain, using the third RF signal and the fourthRF signal, a second mixed RF signal indicative of a second distancebetween the second interrogator and the target device.

Some embodiments provide for a method comprising: transmitting, from afirst interrogator device to a target device, a first radio-frequency(RF) signal having a first center frequency; receiving, at the firstinterrogator device and from the target device, a second RF signalhaving a second center frequency that is a harmonic of the firstfrequency; transmitting, from a second interrogator device to the targetdevice, a third RF signal having the first center frequency; receiving,at the second interrogator device and from the target device, a fourthRF signal having the second center frequency; determining a firstdistance based on the first RF signal and the second RF signal;determining a second distance based on the third RF signal and thefourth RF signal; and determining a location of the target device usingthe determined first distance and second distance.

Some embodiments provide for a device comprising: a transmit antennaconfigured to transmit radio frequency (RF) signals; a receive antennaconfigured to receive RF signals; and circuitry, differentially coupledto the transmit and receive antennas, and configured to provide to thetransmit antenna RF signals to be transmitted by the transmit antennaand to process RF signals received by the receive antenna.

Some embodiments provide for a device comprising: a substrate; atransmit antenna fabricated on the substrate and configured to transmitradio-frequency (RF) signals; a receive antenna fabricated on thesubstrate and configured to receive RF signals; and circuitry, disposedon the substrate and differentially coupled to the transmit and receiveantennas, and configured to provide to the transmit antenna RF signalsto be transmitted by the transmit antenna and to process RF signalsreceived by the receive antenna, wherein the substrate comprisesmaterial for reducing harmonic coupling between the transmit antenna andthe receive antenna.

Some embodiments are directed to a device comprising: a substrate; asemiconductor die flip-chip bonded to the substrate; a transmit antennafabricated on the substrate and configured to transmit microwaveradio-frequency (RF) signals; and circuitry integrated with thesemiconductor die, differentially coupled to the transmit antenna andconfigured to provide to the transmit antenna microwave RF signals to betransmitted by the transmit antenna.

Some embodiments are directed to a device comprising: a substrate; asemiconductor die mounted on the substrate; a transmit antennafabricated on the substrate and configured to transmit microwaveradio-frequency (RF) signals; and circuitry integrated with thesemiconductor die, differentially coupled to the transmit antenna andconfigured to provide to the transmit antenna microwave linear frequencymodulated RF signals to be transmitted by the transmit antenna.

Some embodiments provide for a system comprising: an interrogatordevice, comprising: a first transmit antenna configured to transmitradio-frequency (RF) signals circularly polarized in a first rotationaldirection; and a first receive antenna configured to receive RF signalscircularly polarized in a second rotational direction different from thefirst rotational direction; and a target device, comprising: a secondreceive antenna configured to receive RF signals circularly polarized inthe first rotational direction and a second transmit antenna configuredto transmit, to the interrogator device, RF signals circularly polarizedin the second rotational direction.

Some embodiments provide for a method comprising: transmitting, using afirst transmit antenna, a first radio-frequency (RF) signal circularlypolarized in a first rotational direction; receiving, using a secondreceive antenna, a second RF signal circularly polarized in the firstrotational direction, the second RF signal resulting from propagation ofthe first RF signal; transmitting, using a second transmit antenna, athird RF signal circularly polarized in a second rotational directiondifferent from the first rotational direction, the third signalgenerated using the second RF signal; and receiving, using a firstreceive antenna, a fourth RF signal circularly polarized in the secondrotational direction, the fourth signal resulting from propagation ofthe third RF signal.

Some embodiments provide for a device comprising: a first transmitantenna configured to transmit, to a target device, a firstradio-frequency (RF) signal circularly polarized in a first rotationaldirection; a first receive antenna configured to receive, from thetarget device, a second RF signal circularly polarized in a secondrotational direction different from the first rotational direction; andcircuitry configured to determine a first distance between the deviceand the target device using the first RF signal and the second RFsignal.

Some embodiments provide for a device comprising: a substrate; asemiconductor die mounted on the substrate; a transmit antennafabricated on the substrate and configured to transmit radio-frequency(RF) signals at least at a first center frequency; a receive antennafabricated on the substrate and configured to receive RF signals atleast at a second center frequency different than the first centerfrequency; and circuitry integrated with the semiconductor die andconfigured to provide RF signals to the transmit antenna and to receiveRF signals from the receive antenna.

Some embodiments provide for a device comprising: a substrate; a firsttransmit antenna fabricated on the substrate and configured to transmitradio frequency (RF) signals at least at a first center frequency; afirst receive antenna fabricated on the substrate and configured toreceive RF signals at least at a second center frequency different fromthe first center frequency; a second receive antenna fabricated on thesubstrate and configured to receive RF signals at least at the firstcenter frequency; and a second transmit antenna fabricated on thesubstrate and configured to transmit RF signals at least at the secondcenter frequency; a semiconductor die mounted to the substrate andcoupled to the first transmit antenna, the first receive antenna, thesecond transmit antenna, and the second receive antenna, thesemiconductor die comprising: interrogator circuitry configured toprovide RF signals having the first center frequency to the firsttransmit antenna and to receive RF signals having the second centerfrequency from the first receive antenna; and target device circuitryconfigured to receive RF signals having the first center frequency fromthe second receive antenna and provide RF signals having the secondcenter frequency to the second transmit antenna.

Some embodiments provide for a device comprising: a substrate; asemiconductor die mounted on the substrate; a transmit antennafabricated on the substrate and configured to transmit radio-frequency(RF) signals circularly polarized in a first rotational direction; areceive antenna fabricated on the substrate and configured to receive RFsignals circularly polarized in a second rotational direction differentfrom the first rotational direction; and circuitry integrated with thesemiconductor die and configured to provide RF signals to the transmitantenna and to receive RF signals from the receive antenna.

Some embodiments provide for a device, comprising: a substrate; a firsttransmit antenna fabricated on the substrate and configured to transmitradio frequency (RF) signals circularly polarized in a first rotationaldirection; a first receive antenna fabricated on the substrate andconfigured to receive RF signals circularly polarized in a secondrotational direction different from the first rotational direction; asecond receive antenna fabricated on the substrate and configured toreceive RF signals circularly polarized in the first rotationaldirection; and a second transmit antenna fabricated on the substrate andconfigured to transmit RF signals circularly polarized in the secondrotational direction; a semiconductor die mounted to the substrate andcoupled to the first transmit antenna, the first receive antenna, thesecond transmit antenna, and the second receive antenna, thesemiconductor die comprising: interrogator circuitry configured toprovide RF signals to the first transmit antenna and to receive RFsignals from the first receive antenna; and target device circuitryconfigured to receive RF signals from the second receive antenna andprovide RF signals to the second transmit antenna.

Some embodiments provide for a system comprising: synchronizationcircuitry; a first interrogator device coupled to the synchronizationcircuitry and comprising: a transmit antenna; a first receive antenna;and first circuitry configured to: generate, using radio-frequency (RF)signal synthesis information received from the synchronizationcircuitry, a first RF signal for transmission by the transmit antenna;generate, using the first RF signal and a second RF signal received froma target device by the first receive antenna, a first mixed RF signalindicative of a first distance between the first interrogator and thetarget device; and a second interrogator device coupled to thesynchronization circuitry and comprising: a second receive antenna; andsecond circuitry configured to: generate, using the RF signal synthesisinformation a third RF signal; and generate, using the third RF signaland a fourth RF signal received from the target device by the secondreceive antenna, a second mixed RF signal indicative of a seconddistance between the second interrogator and the target device.

Some embodiments provide for a method comprising: generatingradio-frequency (RF) signal synthesis information; generating a first RFsignal using the RF signal synthesis information; transmitting the firstRF signal to a target device using a transmit antenna; aftertransmitting the first RF signal, receiving a second RF signal from thetarget device using a first receive antenna; generating a third RFsignal using the RF signal synthesis information; receiving a fourth RFsignal from the target device using a second receive antenna;generating, using the first RF signal and the second RF signal, a firstmixed RF signal indicative of a first distance between the first receiveantenna and the target device; and generating, using the third RF signaland the fourth RF signal, a second mixed RF signal indicative of asecond distance between the second receive antenna and the targetdevice.

Some embodiments provide for a device comprising: a receive antennaconfigured to receive a first radio-frequency (RF) signal having a firstcenter frequency; a first transmit antenna configured to transmit asecond RF signal having a second center frequency that is a harmonic ofthe first center frequency; a second transmit antenna configured totransmit a third RF signal having a third center frequency that is aharmonic of the first center frequency and is different from the secondcenter frequency; first circuitry, coupled to the receive antenna and tothe first transmit antenna, configured to generate the second RF signalusing the first RF signal and provide the second RF signal to the firsttransmit antenna for transmission; and second circuitry, coupled to thereceive antenna and to the second transmit antenna, configured togenerate the third RF signal using the first RF signal and provide thethird RF signal to the second transmit antenna for transmission.

Some embodiments provide for a device comprising: a transmit antennaconfigured to transmit, to a target device, a first radio-frequency (RF)signal having a first center frequency; a first receive antennaconfigured to receive, from the target device, a second RF signal havinga second center frequency that is a harmonic of the first centerfrequency; a second receive antenna configured to receive, from thetarget device, a third RF signal having a third center frequency that isa harmonic of the first center frequency and is different from thesecond center frequency; first circuitry configured to obtain, using thefirst RF signal and the second RF signal, a first mixed RF signalindicative of a first distance between the device and the target device;and second circuitry configured to obtain, using the first and third RFsignals, a second mixed RF signal indicative of a second distancebetween the device and the target device.

Some embodiments provide for a device comprise: a first receive antennaconfigured to receive a first radio-frequency (RF) signal having a firstcenter frequency; a second receive antenna configured to receive asecond RF signal having a second center frequency; a first transmitantenna configured to transmit a third RF signal having a third centerfrequency different from each of the first and second centerfrequencies; a second transmit antenna configured to transmit a fourthRF signal having a fourth center frequency different from each of thefirst, second, and third center frequencies; and circuitry comprising: afrequency mixer configured to generate a fifth RF signal by using thefirst RF signal and the second RF signal; first circuitry configured togenerate the third RF signal using the fifth RF signal; and secondcircuitry configured to generate the fourth RF signal using the fifth RFsignal.

Some embodiments provide for a device comprising: a first transmitantenna configured to transmit, to a target device, a firstradio-frequency (RF) signal having a first center frequency; a secondtransmit antenna configured to transmit, to the target device, a secondRF signal having a second center frequency; a first receive antennaconfigured to receive, from the target device, a third RF signal havinga third center frequency different from each of the first and secondcenter frequencies; a second receive antenna configured to receive, fromthe target device, a fourth RF signal having a fourth center frequencydifferent from each of the first, second, and third center frequencies;first circuitry configured to obtain, using the first RF signal, thesecond RF signal, and the third RF signal, a first mixed RF signalindicative of a first distance between the device and the target device;and second circuitry configured to obtain, using the first RF signal,the second RF signal, and the fourth RF signal, a second mixed RF signalindicative of a second distance between the device and the targetdevice.

Some embodiments provide for a device comprising: a substrate; anoscillator disposed on the substrate and configured to generate a firstradio-frequency (RF) signal having a first center frequency; a dual bandantenna mounted on the substrate and configured to receive, from anexternal device different from the device, a second RF signal having asecond center frequency; and a frequency mixer disposed on the dual bandantenna and configured to: generate a third RF signal having a thirdcenter frequency by mixing the first RF signal generated by theoscillator with the second RF signal received by the dual band antenna;and provide the third RF signal to the dual band antenna fortransmission, wherein the dual band antenna is configured to transmitthe third RF signal.

Some embodiments provide for a device comprising: a substrate; anoscillator disposed on the substrate and configured to generateradio-frequency (RF) signals having a first center frequency; a dualband microelectromechanical system (MEMS) antenna mounted on thesubstrate and configured to receive RF signals having a second centerfrequency; and circuitry configured to: generate RF signals having athird center frequency by mixing the RF signals generated by theoscillator with the RF signals received by the dual band MEMS antenna;and provide the RF signals having the third center frequency to the dualband MEMS antenna for transmission.

Some embodiments provide for a device comprising: a substrate; anoscillator disposed on the substrate; a dual band antenna mounted on thesubstrate; and circuitry configured to: generate microwaveradio-frequency (RF) signals by mixing microwave RF signals generated bythe oscillator with microwave RF signals received by the dual bandantenna; and provide the generated microwave RF signals to the dual bandantenna for transmission.

The foregoing is a non-limiting summary of the invention, which isdefined by the attached claims.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments will be described with reference to thefollowing figures. It should be appreciated that the figures are notnecessarily drawn to scale.

FIG. 1A shows an illustrative system 100 that may be used to implementradio frequency (RF) localization techniques, in accordance with someembodiments of the technology described herein.

FIG. 1B shows illustrative components of an interrogator device and atarget device, which are part of the illustrative system 100 shown inFIG. 1A, in accordance with some embodiments of the technology describedherein.

FIG. 2 shows another illustrative system that may be used to implementRF localization techniques, in accordance with some embodiments of thetechnology described herein.

FIG. 3 is a block diagram illustrating components of an interrogatordevice, in accordance with some embodiments of the technology describedherein.

FIGS. 4A and 4B illustrate left- and right-handed circular polarization,respectively.

FIG. 5A is a block diagram illustrating components of an interrogatordevice, in accordance with some embodiments of the technology describedherein.

FIG. 5B is a block diagram illustrating components of an exampledual-mode localization device configured to operate as an interrogatoror as a transponder.

FIG. 6A is a block diagram illustrating components of an interrogatordevice, in accordance with some embodiments of the technology describedherein.

FIG. 6B is a block diagram illustrating components of an target device,in accordance with some embodiments of the technology described herein.

FIG. 7A is a diagram of an illustrative substrate having transmit andreceive antennas fabricated thereon, in accordance with some embodimentsof the technology described herein.

FIG. 7B is a diagram of an illustrative semiconductor die being preparedfor bonding to the substrate of FIG. 7A, in accordance with someembodiments of the technology described herein.

FIG. 7C is a diagram of the illustrative substrate of FIG. 7A after theillustrative semiconductor die of FIG. 7B has been flip-chip bonded tothe substrate, in accordance with some embodiments of the technologydescribed herein.

FIG. 7D is an illustration of one way in which the device of FIG. 7C maybe encapsulated, in accordance with some embodiments of the technologydescribed herein.

FIG. 7E is an illustration of another way in which the device of FIG. 7Cmay be encapsulated, in accordance with some embodiments of thetechnology described herein.

FIG. 7F is an illustration of another way in which the device of FIG. 7Cmay be encapsulated, in accordance with some embodiments of thetechnology described herein.

FIG. 8A is a block diagram illustrating components of transmit andreceive circuitry part of an interrogator device, in accordance withsome embodiments of the technology described herein.

FIG. 8B is a block diagram illustrating components of transmit andreceive circuitry part of another interrogator device, in accordancewith some embodiments of the technology described herein.

FIG. 8C is a block diagram illustrating components of transmit andreceive circuitry part of another interrogator device, in accordancewith some embodiments of the technology described herein.

FIG. 8D is a block diagram illustrating components of transmit andreceive circuitry part of another interrogator device, in accordancewith some embodiments of the technology described herein.

FIG. 9A is a block diagram illustrating components of a target device,in accordance with some embodiments of the technology described herein.

FIG. 9B is a block diagram illustrating components of another type oftarget device, in accordance with some embodiments of the technologydescribed herein.

FIG. 9C is a block diagram illustrating components of another type oftarget device, in accordance with some embodiments of the technologydescribed herein.

FIG. 9D is a block diagram illustrating components of another typetarget device, in accordance with some embodiments of the technologydescribed herein.

FIG. 9E is a block diagram illustrating components of another typetarget device, in accordance with some embodiments of the technologydescribed herein.

FIG. 9F is a block diagram illustrating components of another typetarget device, in accordance with some embodiments of the technologydescribed herein.

FIG. 9G is a diagram illustrating a front view of components of a targetdevice implemented on a printed circuit board, in accordance with someembodiments of the technology described herein.

FIG. 9H is a diagram of illustrating a back view of components of thetarget device of FIG. 9G, in accordance with some embodiments of thetechnology described herein.

FIG. 10 is a block diagram illustrating components of a target devicehaving a single dual band antenna, in accordance with some embodimentsof the technology described herein.

FIG. 11A is a block diagram illustrating components of a multi-spectralinterrogator and a multi-spectral target device, in accordance with someembodiments of the technology described herein.

FIG. 11B is a block diagram illustrating components of another type ofmulti-spectral interrogator and another type of multi-spectral targetdevice, in accordance with some embodiments of the technology describedherein.

FIG. 12A is a diagram illustrating a target device having a localoscillator and a dual-band antenna, in accordance with some embodimentsof the technology described herein.

FIG. 12B is a diagram of a side view of a target device having a localoscillator and a dual band antenna, in accordance with some embodimentsof the technology described herein.

FIG. 13A is a block diagram illustrating waveform generator circuitryconfigured to generate frequency-modulated waveforms using a phaselocked loop, in accordance with some embodiments of the technologydescribed herein.

FIG. 13B is a block diagram illustrating another type of waveformgenerator circuitry configured to generate frequency-modulated waveformsusing a phase locked loop, in accordance with some embodiments of thetechnology described herein.

FIG. 13C is a block diagram illustrating another type of waveformgenerator circuitry configured to generate frequency-modulated waveformsusing a phase locked loop, in accordance with some embodiments of thetechnology described herein.

FIG. 14A is a block diagram of an illustrative localization systemcomprising multiple synchronized interrogator devices including at leastone transmit and receive interrogator device and multiple receive-onlyinterrogator device, in accordance with some embodiments of thetechnology described herein.

FIG. 14B is a block diagram of another illustrative localization systemcomprising multiple synchronized interrogator devices including at leastone transmit and receive interrogator device and multiple receive-onlyinterrogator device, in accordance with some embodiments of thetechnology described herein.

FIG. 14C is a block diagram of a receive-only interrogator device partof the illustrative localization system of FIG. 14A, in accordance withsome embodiments of the technology described herein.

FIG. 14D is a block diagram of a receive-only interrogator device partof the illustrative localization system of FIG. 14B, in accordance withsome embodiments of the technology described herein.

FIG. 15 is a flowchart of an illustrative process for determining thelocation of a target device using measurements made by at least twointerrogator devices, in accordance with some embodiments of thetechnology described herein.

FIG. 16 is a flowchart of an illustrative process for making distancemeasurements using an interrogator device configured to transmit RFsignals circularly polarized in one rotational direction and receive RFsignals circularly polarized in another rotational direction, inaccordance with some embodiments of the technology described herein.

FIG. 17 is a flowchart of an illustrative process for determining thelocation of a target device using multiple synchronized interrogatordevices including at least one master interrogator device and areceive-only interrogator device, in accordance with some embodiments ofthe technology described herein.

DETAILED DESCRIPTION

Determining the location of an object or target (also referred to hereinas localization) has an array of applications in a number of fields. Forexample, the ability to locate and/or track an object at very smallscales (i.e., at high resolutions) facilitates advancement of numerousapplications, and has wide spread applicability to a number of differentfields. For example, the ability to accurately and precisely track anobject or target in real-time has numerous benefits in the gamingindustry and, in particular, for interactive video games. Objectlocalization also has many applications in autonomous systems, such asautonomous vehicle navigation, exploration, robotics and human machineinteraction. Virtual reality, motion tracking and capture and the likealso benefit from the ability to locate and/or track object(s)accurately, robustly and in real-time or near real-time. Details ofusing localization techniques in a variety of applications are describedin U.S. patent application Ser. No. 15/181,930 titled “High-PrecisionTime of Flight Measurement Systems,” filed on Jun. 14, 2016, U.S. patentapplication Ser. No. 15/181,956 titled “High Precision Motion Trackingwith Time of Flight Measurement Systems,” filed on Jun. 14, 2016, U.S.patent application Ser. No. 15/181,978 titled “High Precision SubsurfaceImaging and Location Mapping with Time of Flight Measurement Systems,”filed on Jun. 14, 2016, and U.S. patent Ser. No. 15/181,999 titled“High-Precision Time of Flight Measurement System for IndustrialAutomation,” filed on Jun. 14, 2016, each of which is hereinincorporated by reference in its entirety.

Conventional techniques for target localization have substantialdrawbacks and are often inadequate for many (or most) of theseapplications and/or perform unsatisfactorily in all but very limitedcircumstances or controlled environments. In particular, conventionallocalization techniques suffer from one or more drawbacks thatsignificantly limit their use and/or applicability, includinginsufficient accuracy, low signal-to-noise (SNR) ratio, relativelylengthy refresh rates, susceptibility to background clutter, high cost,large size, etc. As a result, conventional localization techniquesgenerally have narrow and limited application. The inventors havedeveloped localization techniques with broad applicability to a range offields that are suitable for a wide variety of applications.

For many applications, high localization accuracy (resolution) is animportant capability and is a limiting factor for many conventionallocalization techniques. The inventors have developed localizationtechniques with the ability to resolve the location of a target in themillimeter and sub-millimeter range, referred to herein generally asmicro-localization. According to some embodiments, a micro-localizationsystem comprises an interrogator configured to transmit a radiofrequency (RF) signal (e.g., a microwave or millimeter wave RF signal)and a target configured to, in response to receiving the RF signal,transmit an RF signal to be received by the interrogator. The RF signalreceived from the target by the interrogator is used to determine thedistance between the interrogator and the target.

FIG. 1A illustrates an exemplary micro-localization system 100, inaccordance with some embodiments. Micro-localization system 100comprises a plurality of interrogator devices 102, one or more of whichare configured to transmit an RF signal 103 (e.g., RF signals 103 a, 103b, 103 c, etc.). System 100 also comprises one or more target devices104 configured to receive RF signals 103 and, in response, transmit RFsignals 105 (e.g., RF signals 105 a, 105 b and 105 c, etc.).Interrogator devices 102 are configured to receive RF signals 105 thatare then used to determine distances between respective interrogator andtarget devices. The computed distances may be used to determine thelocation of one or more target devices 104, a number of techniques ofwhich are described in further detail below. It should be appreciatedthat while multiple target devices 104 are illustrated in FIG. 1A, asingle target device may be utilized. More generally, it should beappreciated that any number of interrogator devices 102 and targetdevices 104 may be used, as the aspects of the technology describedherein are not limited in this respect.

Micro-localization system 100 may also include a controller 106configured to communicate with interrogator devices 102 and targetdevices 104 via communication channel 108, which may include a network,device-to-device communication channels, and/or any other suitable meansof communication. Controller 106 may be configured to coordinate thetransmission and/or reception of RF signals 103 and 105 between desiredinterrogator and target devices via communication channels 107 a, 107 band 108, which may be a single communication channel or include multiplecommunication channels. Controller 106 may also be configured todetermine the location of one or more target devices 104 frominformation received from interrogator devices 102. As discussed infurther detail below, controller 106 may be implemented as a standalonecontroller or may be implemented in full or in part by one or moreinterrogator devices 102 and/or target devices 104. Different exemplaryconfigurations and implementations for micro-localization system 100 aredescribed in further detail below, but are not limited to theconfigurations discussed herein.

Resolving the location of a target with a high degree of accuracydepends in part on receiving the RF signals transmitted by the targetwith high fidelity and, in part, on the ability to distinguish the RFsignals transmitted by a target device from RF signals transmitted by aninterrogator device, background clutter, and/or noise. The inventorshave developed techniques for improving the signal-to-noise ratio of thesignals received by the interrogator and target devices to facilitatemicro-localization of one or more target devices. As one example, theinventors recognized that by configuring the interrogator and targetdevices to transmit at different frequencies, localization performancecould be improved. According to some embodiments, one or moreinterrogator devices transmit first RF signals (e.g., RF signals 103)having a first center frequency and, in response to receiving the firstRF signals, one or more target devices transmit second RF signals (e.g.,RF signals 105) having a second center frequency different from thefirst center frequency. In this manner, receive antennas on the one ormore interrogator devices can be configured to respond to RF signalsabout the second center frequency, improving the ability of theinterrogator devices to receive RF signals from target devices incluttered and/or noisy environments.

The inventors further recognized that relatively simple and/or costeffective circuitry could be implemented at the target device totransform RF signals having a first center frequency received from aninterrogator device to RF signals having a second center frequencydifferent from the first center frequency for transmission. According tosome embodiments, the second center frequency is harmonically related tothe first center frequency. For example, in system 100 illustrated inFIG. 1A, a target device 104 may be configured to transform RF signals103 and transmit RF signals 105 at a harmonic of the center frequency ofthe received RF signal 103. According to other embodiments, a targetdevice transforms RF signals having a first center frequency receivedfrom an interrogator device to RF signals having second center frequencythat is different from, but not harmonically related to the first centerfrequency. In other embodiments, a target device is configured togenerate RF signals at a second center frequency different from thefirst center frequency, either harmonically or not harmonically related,rather than transforming RF signals received from an interrogatordevice. Exemplary techniques for transmitting RF signals, frominterrogator and target devices, having different respective centerfrequencies are discussed in further detail below.

The inventors have further recognized that changing the polarization ofRF signals transmitted by interrogator and target devices, respectively,may be used to improve SNR and allow interrogator devices to receive RFsignals transmitted by target devices with improved fidelity,facilitating micro-localization even in cluttered and/or noisyenvironments. According to some embodiments, one or more interrogatordevices are configured to transmit first RF signals circularly polarizedin a first rotational direction (e.g., clockwise) and, in response toreceiving the first RF signals, one or more target devices areconfigured to transmit second RF signals circularly polarized in asecond rotational direction different from the first rotationaldirection (e.g., counter-clockwise). A target device may be configuredto transform the polarization of received RF signals or may beconfigured to generate RF signals circularly polarized in the secondrotation direction, as aspects of the technology described herein arenot limited in this respect. Exemplary techniques for transmitting RFsignals, from interrogator and target devices, circularly polarized indifferent respective rotational directions are discussed in furtherdetail below.

Many conventional localization techniques achieve desired performancecharacteristics by using expensive electronic components, which areoften large, relatively complex and/or consume relatively significantamounts of power. As a result, such conventional techniques do notprovide a general-purpose localization solution capable of beingemployed in a wide range of applications. To address this drawback, theinventors have developed a chip-scale micro-localization system in whichinterrogator and target devices are fabricated as individual packaged orpartially packaged devices capable of being integrated in virtually anysystem for use in a wide variety of applications. The inventors havedeveloped designs for the components of a micro-localization system(e.g., interrogator and target devices) that allow for their fabricationon a silicon die and/or on or within the device package, facilitatingthe production of chip-scale components of a micro-localization systemthat can be inexpensively produced at large volume and integrated intovirtually any system for which micro-localization is desired.

As discussed above, many conventional localization techniques sufferfrom low SNR and, as a result, are limited in the range in which thelocalization techniques can operate and/or may exhibit lengthy refreshtimes (e.g., the interval of time between successive computations of thelocation of a target) due, at least in part, to the need to repeatedlyinterrogate the target to build up enough signal to adequately determinethe distance to the target. The inventors have developed techniques toimprove SNR that substantially increase the range at whichmicro-localization can be performed (i.e., increase the distance betweeninterrogator and target devices at which the system can micro-locate thetarget device). Referring again to the exemplary micro-localizationsystem 100 illustrated in FIG. 1A, an interrogator device 102 may beconfigured to transmit first RF signals and receive second RF signalstransmitted by one or more target devices in response. Accordingly, aninterrogator device may comprise a transmit antenna for transmitting thefirst RF signals and a receive antenna for receiving second RF signals.Any RF signals generated for transmission by and/or transmitted by theinterrogator's transmit antenna that are also detected by theinterrogator's receive antenna interfere with the ability of the receiveantenna to detect RF signals being transmitted by one or more targetdevices. For example, any portion of an RF signal generated by aninterrogator for transmission that is picked up by the interrogator'sreceive antenna operates as noise that decreases the SNR (or asinterference decreasing the SINR, which is the signal to interferenceplus noise ratio), effectively drowning out the RF signals beingtransmitted by a target device, and reduces the range at which theinterrogator can determine the location of the target device.

To increase the SNR, the inventors have developed a number of techniquesto reduce the amount and/or impact of signal detection by the receiveantenna of RF signals generated by interrogator device for transmissionby and/or transmitted by the transmit antenna (or by the transmitantenna of a proximately located interrogator or target devices). Asdiscussed above, transmitting and receiving at different centerfrequencies facilitate signal differentiation, but also reducesinterference between transmit and receive antennas. However, receiveantennas remain susceptible to detection of transmitted signals, forexample, harmonics that are transmitted from the transmit antenna. Theinventors have further recognized that transmitting and receiving atdifferent circular polarizations, as discussed above, further reducesinterference between transmit and receive channels. The inventors havefurther recognized that differentially coupling a receive antenna and/ora transmit antenna to transmit/receive circuitry of the interrogatordevice reduces the amount of interference between the transmit andreceive channels. Similar differential coupling can be implemented atthe target device for the same purpose. The inventors have furtherappreciated that, for example, using chip-scale technology, thesubstrate of an interrogator or target device (e.g., one or more layerswithin or on the substrate of the device package) may include afrequency selective surface to reduce interference (e.g., to reduceharmonic coupling) between transmit and receive antennas and/or thesubstrate may be fabricated or treated with an absorbent coating thatabsorbs RF signals from the transmit antenna to reduce interference. Oneor any combination of these techniques may be used to reduceinterference and increase SNR. According to some embodiments, techniquesfor increasing SNR described herein facilitate micro-localization at adistance of up to approximately 20-40 (e.g., 30) meters. The inventorshave developed numerous techniques that provide for a robust andrelatively inexpensive micro-localization system capable of beingemployed in a wide variety of applications. According to someembodiments, a micro-localization system using techniques describedherein are capable of resolving the location of a target device withaccuracy in the millimeter or sub-millimeter range in virtually anyenvironment. In addition, using the techniques described herein,location of a target can be determined in milliseconds, a millisecond,or less, facilitating real-time tracking of targets that are rapidlymoving. Techniques developed by the inventors, including chip-scalefabrication of micro-localization components, facilitate ageneral-purpose micro-localization system that can be manufactured atrelatively low cost and high volume and that can be convenientlyintegrated in a variety of application level systems. These and othertechniques are discussed in further detail below in connection exemplarymicro-localization systems, in accordance with some embodiments.

It should be appreciated that the techniques introduced above anddiscussed in greater detail below may be implemented in any of numerousways, as the techniques are not limited to any particular manner ofimplementation. Examples of details of implementation are providedherein solely for illustrative purposes. Furthermore, the techniquesdisclosed herein may be used individually or in any suitablecombination, as aspects of the technology described herein are notlimited to the use of any particular technique or combination oftechniques.

FIG. 1B shows illustrative components of an illustrative interrogatordevice 102 and a illustrative target device 104, which are part of theillustrative system 100 shown in FIG. 1A, in accordance with someembodiments of the technology described herein. As shown in FIG. 1B,illustrative interrogator device 102 includes waveform generator 110,transmit and receive circuitry 112, transmit antenna 114, receiveantenna 116, control circuitry 118, and external communications module120. It should be appreciated that, in some embodiments, an interrogatordevice may include one or more other components in addition to orinstead of the components illustrated in FIG. 1B. Similarly, in someembodiments, a target device may include one or more other components inaddition to or instead of the components illustrated in FIG. 1B.

In some embodiments, waveform generator 110 may be configured togenerate RF signals to be transmitted by the interrogator 102 usingtransmit antenna 114. Waveform generator 110 may be configured togenerate any suitable type(s) of RF signals. In some embodiments,waveform generator 110 may be configured to generate frequency modulatedRF signals, amplitude modulated RF signals, and/or phase modulated RFsignals. Non-limiting examples of modulated RF signals, any one or moreof which may be generated by waveform generator 110, include linearfrequency modulated signals (also termed “chirps”), non-linearlyfrequency modulated signals, binary phase coded signals, signalsmodulated using one or more codes (e.g., Barker codes, bi-phase codes,minimum peak sidelobe codes, pseudo-noise (PN) sequence codes,quadri-phase codes, poly-phase codes, Costas codes, Welti codes,complementary (Golay) codes, Huffman codes, variants of Barker codes,Doppler-tolerant pulse compression signals, impulse waveforms, noisewaveforms, and non-linear binary phase coded signals. Waveform generator110 may be configured to generate continuous wave RF signals or pulsedRF signals. Waveform generator 110 may be configured to generate RFsignals of any suitable duration (e.g., on the order of microseconds,milliseconds, or seconds).

In some embodiments, waveform generator 110 may be configured togenerate microwave and/or millimeter wave RF signals. For example,waveform generator 110 may be configured to generate RF signals having acenter frequency in a given range of microwave and/or millimeterfrequencies (e.g., 4-6 GHz, 50-70 GHz). It should be appreciated that anRF signal having a particular center frequency is not limited tocontaining only that particular center frequency (the RF signal may havea non-zero bandwidth). For example, waveform generator 110 may beconfigured to generate a chirp having a center frequency of 60 GHz whoseinstantaneous frequency varies from a lower frequency (e.g., 59 GHz) toan upper frequency (e.g., 61 GHz). Thus, the generated chirp has acenter frequency of 60 GHz and a bandwidth of 2 GHz and includesfrequencies other than its center frequency.

In some embodiments, waveform generator 110 may be configured togenerate RF signals using a phase locked loop. Such configurations aredescribed herein including with reference to FIGS. 8B, 8C, 8D, 13A, 13B,and 13C. In some embodiments, the waveform generator may be triggered togenerate an RF signal by control circuitry 118 and/or in any othersuitable way.

In some embodiments, transmit and receive circuitry 112 may beconfigured to provide RF signals generated by waveform generator 110 totransmit antenna 114. Additionally, transmit and receive circuitry 112may be configured to obtain and process RF signals received by receiveantenna 116. In some embodiments, transmit and receive circuitry 112 maybe configured to: (1) provide a first RF signal to the transmit antenna114 for transmission to a target device (e.g., RF signal 111); (2)obtain a responsive second RF signal received by the receive antenna 116(e.g., RF signal 113) and generated by the target device in response tothe transmitted first RF signal; and (3) process the received second RFsignal by mixing it (e.g., using a frequency mixer) with a transformedversion of the first RF signal. Such processing and associated and otherarchitectures of the transmit and receive circuitry 112 are describedherein including with reference to FIGS. 8A-8D and 11A-11B. The transmitand receive circuitry 112 may be configured to provided processed RFsignals to control circuitry 118, which may (with or without performingfurther processing the RF signals obtained from circuitry 112) providethe RF signals to external communications module 120.

In some embodiments, each of transmit antenna 114 and receive antenna116 may be a patch antenna, a planar spiral antenna, an antennacomprising a first linearly polarized antenna and a second linearlypolarized antenna orthogonally disposed to the first linearly polarizedantenna, a MEMS antenna, a dipole antenna, or any other suitable type ofantenna configured to transmit or receive RF signals. Each of transmitantenna 114 and receive antenna 116 may be directional or isotropic(omnidirectional). Transmit antenna 114 and receive antenna 116 may thesame type or different types of antennas.

In some embodiments, transmit antenna 114 may be configured to radiateRF signals circularly polarized in one rotational direction (e.g.,clockwise) and the receive antenna 116 may be configured to receive RFsignals circularly polarized in another rotational direction (e.g.,counter-clockwise). In some embodiments, transmit antenna 114 may beconfigured to radiate RF signals having a first center frequency (e.g.,RF signal 111 transmitted to target device 104) and the receive antennamay be configured to receive RF signals having a second center frequencydifferent from (e.g., a harmonic of) the first center frequency (e.g.,RF signal 113 received from target device 104 and generated by targetdevice 104 in response to receiving the RF signal 111).

In some embodiments, transmit antenna 114 and receive antenna 116 arephysically separate antennas. In other embodiments, however, theinterrogator 102 may include a dual mode antenna configured to operateas a transmit antenna in one mode and as a receive antenna in anothermode.

In some embodiments, control circuitry 118 may be configured to triggerthe waveform generator 110 to generate an RF signal for transmission bythe transmit antenna 114. The control circuitry 118 may trigger thewaveform generator in response to a command to do so received byexternal communications interface 120 and/or based on logic part ofcontrol circuitry 118.

In some embodiments, control circuitry 118 may be configured to receiveRF signals from transmit and receive circuitry 112 and forward thereceived RF signals to external communications interface 120 for sendingto controller 106. In some embodiments, control circuitry 118 may beconfigured to process the RF signals received from transmit and receivecircuitry 112 and forward the processed RF signals to externalcommunications interface 120. Control circuitry 118 may perform any ofnumerous types of processing on the received RF signals including, butnot limited to, converting the received RF signals to from analog todigital (e.g., by sampling using an ADC), performing a Fourier transformto obtain a time-domain waveform, estimating a time of flight betweenthe interrogator and the target device from the time-domain waveform,and determining an estimate of distance between the interrogator 102 andthe target device that the interrogator 102 interrogated. The controlcircuitry 118 may be implemented in any suitable way and, for example,may be implemented as an application specific integrated circuit (ASIC),a field programmable gate array (FPGA), a combination of logic circuits,a microcontroller, or a microprocessor.

External communications module 120 may be of any suitable type and maybe configured to communicate according to any suitable wirelessprotocol(s) including, for example, a Bluetooth communication protocol,an IEEE 802.15.4-based communication protocol (e.g., a “ZigBee”protocol), and/or an IEEE 802.11-based communication protocol (e.g., a“WiFi” protocol).

As shown in FIG. 1B, target device 104 includes receive antenna 122,signal transformation circuitry 124, transmit antenna 126, controlcircuitry 128, and external communications module 130.

In some embodiments, each of receive antenna 122 and transmit antenna126 may be a patch antenna, a planar spiral antenna, an antennacomprising a first linearly polarized antenna and a second linearlypolarized antenna orthogonally disposed to the first linearly polarizedantenna, a MEMS antenna, a dipole antenna, or any other suitable type ofantenna configured to receive or transmit RF signals. Each of receiveantenna 122 and transmit antenna 126 may be directional or isotropic.Receive antenna 122 and transmit antenna 126 may the same type ordifferent types of antennas. In some embodiments, receive antenna 122and transmit antenna 126 may be separate antennas. In other embodiments,a target device may include a dual mode antenna operating as a receiveantenna in one mode and as a transmit antenna the other mode.

In some embodiments, receive antenna 122 may be configured to receive RFsignals circularly polarized in one rotational direction (e.g.,clockwise) and the transmit antenna 126 may be configured to transmit RFsignals circularly polarized in another rotational direction (e.g.,counter-clockwise).

In some embodiments, receive antenna 122 may be configured to receive RFsignals having a first center frequency. The received RF signals may betransformed by signal transformation circuitry 124 to obtainedtransformed RF signals having a second center frequency different from(e.g., a harmonic of) the first center frequency. Such processing andassociated and other architectures of the signal transformationcircuitry 124 are described herein including with reference to FIGS.9A-9H, 10, 11A-B, and 12A-B. The transformed RF signals having thesecond center frequency may be transmitted by transmit antenna 126.

In some embodiments, each of the transmit and/or the receive antennas onan interrogator may be directional antennas. This may be useful inapplications where some information is known about the region of spacein which the target device is located (e.g., the target device islocated in front of the interrogator, to the front left of theinterrogator, etc.). Even if the target device is attached to a movingobject (e.g., an arm of an industrial robot, a game controller), themovement of the target device may be constrained so that the targetdevice is always within a certain region of space relative to theinterrogator so that using directional antennas to focus on that regionof space increases the sensitivity of the interrogator to signalsgenerated by the target device. In turn, this increases the distancebetween the interrogator and target device at which themicro-localization system may operate with high accuracy. However, itshould be appreciated that in some embodiments, the antennas on aninterrogator may be isotropic (omnidirectional), as aspects of thetechnology describe herein are not limited in this respect.

In some embodiments, each of the transmit and/or the receive antennas onthe target device may be isotropic so that the target device may beconfigured to receive signals from and/or provide RF signals to aninterrogator located in any location relative to the target device. Thisis advantageous because, in some applications of micro-localization, thetarget device may be moving and its relative orientation to one or moreinterrogators may not be known in advance. However, in some embodiments,the antennas on a target device may be directional (anisotropic), asaspects of the technology describe herein are not limited in thisrespect.

In some embodiments, control circuitry 128 may be configured to turn thetarget device 104 on or off (e.g., by powering off one or morecomponents in signal transformation circuitry 124) in response to acommand to do so received via external communications interface 130. Thecontrol circuitry 128 may be implemented in any suitable way and, forexample, may be implemented as an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA), a combination oflogic circuits, a microcontroller, or a microprocessor. Externalcommunications module 130 may be of any suitable type including any ofthe types described herein with reference to external communicationsmodule 120.

As discussed above with reference to FIG. 1A, multiple interrogatordevices may be utilized in order to determine a location of a targetdevice. In some embodiments, each of the interrogator devices may beconfigured to transmit an RF signal to a target device, receive aresponsive RF signal from the target device (the responsive signal mayhave a different polarization and/or a different center frequency fromthe signal that was transmitted), and process the transmitted RF signaltogether with the received RF signal to obtain an RF signal indicativeof the distance between the interrogator device and the target device.The RF signals indicative of the distances between the interrogatordevices and the target device may be processed (e.g., by theinterrogators or another processor) to obtain estimates of the distancesbetween the target device and each of the interrogators. In turn, theestimated distances may be used to determine the location of the targetdevice in 3D space.

FIG. 15 is a flowchart of an illustrative process 1500 for determiningthe location of a target device using measurements made by at least twointerrogator devices, in accordance with some embodiments of thetechnology described herein. Process 1500 may be executed by anysuitable localization system described herein including, for example,system 100 described with reference to FIG. 1A or system 200 describedwith reference to FIG. 2.

Process 1502 begins at act 1502, where a first interrogator devicetransmits a first RF signal having a first center frequency to a targetdevice. For example, an interrogator device 102 of system 100 may sendRF signal 103 a to target device 104. The RF signal may be of anysuitable type and, for example, may be a linear frequency modulated RFsignal or any other suitable type of RF signal including any of thetypes of signals described herein. The first RF signal transmitted atact 1502 may have any suitable center frequency. For example, the centerfrequency may be any frequency in the range of 50-70 GHz (e.g., 60 GHz)or any frequency in the range of 4-6 GHz (e.g., 5 GHz). The first RFsignal transmitted at act 1502 may be circularly polarized in theclockwise or counterclockwise direction. Circular polarization isdescribed further herein including with reference to FIGS. 4A and 4B.

At act 1504, the first interrogator device that, at act 1502,transmitted an RF signal to a target device, may receive a responsivesecond RF signal from the target device. For example, the interrogatordevice 102 of system 100 may receive second RF signal 105 a from targetdevice 104. The responsive second RF signal may be a transformed versionof the transmitted first RF signal. The target device may generate theresponsive RF signal by receiving and transforming the transmitted RFsignal according to any of the techniques described herein.

In some embodiments, the frequency content of the responsive second RFsignal received at act 1504 may be different from that of thetransmitted RF signal transmitted at act 1502. For example, when thetransmitted RF signal has a first center frequency, the responsive RFsignal may have a second center frequency different from the firstcenter frequency. For example, the second center frequency may be aharmonic of the first center frequency (e.g., the second centerfrequency may be an integer multiple of, such as twice as, the firstcenter frequency). As one example, if the center frequency of thetransmitted first RF signal were 60 GHz, then the center frequency ofthe responsive second RF signal may be 120 GHz, 180 GHz, or 240 GHz. Insome embodiments, the polarization of the responsive second RF signalmay be different from the polarization of the transmitted first RFsignal. For example, when the transmitted first RF signal is circularlypolarized in a clockwise direction, the received second RF signal may becircularly polarized in a counter-clockwise direction. Alternatively,when the transmitted first RF signal is circularly polarized in acounter-clockwise direction, the received second RF signal may becircularly polarized in a clockwise direction.

At act 1506, an estimate of the distance between the first interrogatorand the target device may be determined by using the first RF signaltransmitted at act 1502 and the second RF signal received at act 1504.This may be done in any suitable way. For example, in some embodiments,the first and second RF signals may be mixed (e.g., using a frequencymixer onboard the first interrogator device) to obtain a mixed RFsignal. The mixed RF signal may be indicative of the time of flight and,consequently, the distance between the first interrogator and the targetdevice. The mixed RF signal may be sampled (e.g., using an ADC) and aFourier transform (e.g., an inverse discrete Fourier transform) may beapplied to the samples to obtain a time-domain waveform. The time-domainwaveform may be processed to identify the time of flight of an RF signalbetween the first interrogator and the target device. In someembodiments, the time-domain waveform may be processed to identify thetime of flight by identifying a first time when a responsive RF signalgenerated by the target device is detected by the interrogator. This maybe done in any suitable way. For example, the time-domain waveform mayinclude multiple separated “peaks” (e.g., multiple Gaussian-like bumpseach having a respective peak above the noise floor) and the location ofthe first such peak may indicate the first time when the responsive RFsignal generated by the target is detected by the interrogator. Thisfirst time represents an estimate of the time of flight between theinterrogator and target device. In turn, the estimate of the time offlight between the interrogator and the target device may be convertedto an estimate of the distance between the interrogator and the targetdevice.

Accordingly, in some embodiments: (1) an interrogator may transmit an RFsignal to a target device and receive, from the target device, aresponsive RF signal; (2) a version of the transmitted RF signal may bemixed with the received RF signal to obtain a mixed RF signal; (3) themixed RF signal may be sampled using an ADC to obtain a sampled signal;(4) the sampled signal may be transformed by an inverse discrete Fouriertransform to obtain a time-domain waveform¹; (5) the time-domainwaveform may be processed to identify the time of flight between theinterrogator and the target device; and (6) the time of flight may beconverted to an estimate of the distance between the interrogator andthe target device. ¹ The steps of mixing a received RF signal with aversion of the transmitted RF signal and subsequently applying a Fouriertransform constitute steps of pulse compression processing. Thus, thedevice(s) performing these steps may be said to perform pulsecompression.

It should be appreciated that while all of these acts 1-6 may beperformed on a single device (e.g., the interrogator), this is not alimitation of aspects of the technology described herein. For example,in some embodiments, an interrogator may not include an ADC, and steps3-6 may be performed by one or more devices external to an interrogator.Even in embodiments where the interrogator includes an ADC, the acts 4-6may be performed by one or more device (e.g., a processor) external tothe interrogator.

At act 1508, where a second interrogator device (different from thefirst interrogator device) transmits a third RF signal having the firstcenter frequency to the target device (the same target device to whichthe first RF signal was transmitted and from which the second RF signalwas received). The third RF signal may be of any suitable type and, forexample, may be a linear frequency modulated RF signal or any othersuitable type of RF signal including any of the types of signalsdescribed herein. The third RF signal may have the same center frequencyas the first RF signal and may be circularly polarized in the samedirection as the first RF signal.

At act 1510, the second interrogator device that, at act 1508,transmitted the third RF signal to the target device, may receive aresponsive fourth RF signal from the target device. The responsivefourth RF signal may be a transformed version of the transmitted thirdRF signal. The target device may generate the responsive fourth RFsignal by receiving and transforming the transmitted third RF signalaccording to any of the techniques described herein. In someembodiments, the frequency content of the responsive fourth RF signalreceived at act 1510 may be different from that of the transmitted thirdRF signal transmitted at act 1508. For example, when the transmittedthird RF signal has a first center frequency (e.g., the same centerfrequency as the first RF signal), the responsive fourth RF signal mayhave a second center frequency that is different from and is a harmonicof the first center frequency (e.g., the same center frequency as thesecond RF signal). In some embodiments, the polarization of theresponsive RF fourth signal may be different from the polarization ofthe transmitted third RF signal. For example, when the third transmittedRF signal is circularly polarized in a clockwise direction, the receivedfourth RF signal may be circularly polarized in a counter-clockwisedirection.

At act 1512, an estimate of the distance between the second interrogatorand the target device may be determined by using the third RF signaltransmitted at act 1508 and the fourth RF signal received at act 1510.This may be done in any suitable way including in any of the waysdescribed above with reference to act 1506.

At act 1514, the location of the target device may be determined usingthe distance between the first interrogator and the target deviceobtained at act 1506, the distance between the second interrogator andthe target device obtained at act 1512, and known locations of the firstand second interrogators. This determination may be made in any suitableway and, for example, may be made using any of numerous types ofgeometric methods, least-squares methods, and/or in any of the waysdescribed in U.S. patent application Ser. No. 15/181,930 titled“High-Precision Time of Flight Measurement Systems,” filed on Jun. 14,2016, U.S. patent application Ser. No. 15/181,956 titled “High PrecisionMotion Tracking with Time of Flight Measurement Systems,” filed on Jun.14, 2016, U.S. patent application Ser. No. 15/181,978 titled “HighPrecision Subsurface Imaging and Location Mapping with Time of FlightMeasurement Systems,” filed on Jun. 14, 2016, and U.S. patent Ser. No.15/181,999 titled “High-Precision Time of Flight Measurement System forIndustrial Automation,” filed on Jun. 14, 2016, each of which is hereinincorporated by reference in its entirety.

It should be appreciated that process 1500 is illustrative and thatthere are variations. For example, in some embodiments, more than twointerrogators may be used to interrogate a single target device. In suchembodiments, estimates of distances between the target device and eachof the three or more interrogators may be used to obtain the 2D locationof the target devices (e.g. to specify a 2D plane containing the 3Dtarget devices). When distances between at least three interrogatordevices and a target device are available, then the 3D location of thetarget device may be determined.

FIG. 2 shows an illustrative system 200 that may be used to implement RFlocalization techniques, in accordance with some embodiments of thetechnology described herein. The illustrative system 200 comprises aplurality of interrogators, which are part of a product 202. Theinterrogators may be used to obtain estimates of distance to one or moreof the target devices 225. In turn, these distance estimates (e.g.,together with the known locations of the interrogators on PCB 204relative to one another) may be used to estimate the location(s) of thetarget device(s) 225.

As shown in FIG. 2, product 202 comprises a printed circuit board 204.Master interrogator module 206 having interrogator 214 is disposed onPCB 204 along with interrogators 216, 218, and 220, which may be called“slave” interrogators. Master interrogator module 206 further comprisestiming circuitry 208, control circuitry 210, and communicationscircuitry 212.

The product 202 may be any product (e.g., any consumer or commercialproduct) having a circuit board onto which one or multiple interrogatordevices may be mounted. The circuit board may be rigid or flexible. Forexample, the product 202 may be a computer (e.g., a desktop, a laptop, atablet, a personal digital assistant, etc.) and the PCB 204 may be amotherboard in the computer. As another example, product 202 may be asmartphone and the PCB 204 may be a rigid board or a flex circuit withinthe smartphone. As another example, product 202 may be a camera (e.g.,video camera, a camera for taking still shots, a digital camera, etc.)and the PCB 204 may be a circuit board within the camera. As anotherexample, the product 202 may be a gaming system and the PCB 204 may be acircuit board within the gaming system. As another example, the PCB 204may comprise a flexible circuit ribbon having one or more interrogatorsdisposed thereon, which ribbon may be within product 202, affixed to theside of product 202 (e.g., on the side of a gaming system), or affixednear the product 202 (e.g., affixed on a wall in a room containing theproduct).

Although there are four interrogators shown as part of product 202, inother embodiments, any other suitable number of interrogators may beused (e.g., one, two, three, five, six, seven, eight, nine, ten, etc.),as aspects of the technology described herein are not limited in thisrespect. Each of interrogators 214, 216, 218, and 220 may be of anysuitable type described herein. In some embodiments, the interrogators214, 216, 218, and 220 may be the same type of interrogator. In otherembodiments, at least two of these interrogators may be of differenttypes. For example, in some embodiments, the interrogator 214 may beconfigured to transmit RF signals to a target device 225 and receive RFsignals from the target device, whereas the interrogators 216, 218, and220 may be receive-only interrogators configured to receive RF signalsfrom the target device 225, but which are not capable of transmitting RFsignals to target device 225 (e.g., because these interrogators may notinclude transmit circuitry for generating RF signals for transmission bya transmit antenna and/or the transmission antenna). It should also beappreciated that each of target devices 225 may be of any suitabletype(s) described herein, as aspects of the technology described hereinare not limited in this respect.

In some embodiments, the master interrogator module 206 module may beconfigured to manage operation of the interrogators 214, 216, 218, and220, and/or of target device(s) 225. Module 206 may be configured tomanage each of interrogators 214, 216, 218, and 220 by controlling(e.g., via wires on product PCB 204 and/or wirelessly) when each ofthese interrogators is to transmit RF signals to one or more of targetdevices 225 and receive RF signals from the target device(s) 225.Additionally, module 206 may be configured to control (e.g., using oneor more wireless links maintained by communications circuitry 212) whichof the target devices 225 are on and which of the target devices 225 areoff. In this way, the master interrogator module 206 may selectparticular target device(s) 225 to be interrogated, determine when theparticular target device(s) 225 are to be interrogated, and/or determinewhich of the interrogators onboard PCB 204 are to be used forinterrogating the target device(s) 225.

In some embodiments, the master interrogator module 206 may control theinterrogators 214, 216, 218 and 220 to operate according to a schedulespecifying an order for operating the interrogators in a one-at-a-timemanner. For example, the master interrogator module 206 may control theinterrogators to operate in accordance with a round-robin schedule,whereby the master interrogator controls each of the interrogatorsonboard PCB 204 to transmit an RF signal to a target device (or multipletarget devices) and receive responsive RF signals waveform in aone-at-a-time manner. As one example, master interrogator module 206may: (1) wirelessly communicate with a specific target device 225 toturn it on; (2) trigger interrogator 214 to transmit an RF signal (e.g.,a linear frequency modulated chirp) to the specific target device andreceive a responsive RF signal from the specific target device; (3)after interrogator 214 completes transmitting, trigger interrogator 216to transmit an RF signal to the specific target device and receive aresponsive RF signal from the specific target device; (4) afterinterrogator 216 completes transmitting, trigger interrogator 218 totransmit an RF signal to the specific target device and receive aresponsive RF signal from the specific target device; and (5) afterinterrogator 218 completes transmitting, trigger interrogator 220 totransmit an RF signal to the target device and receive a responsive RFsignal from the target device. When operating according to a round-robinschedule, if each of the interrogators transmits a 1 ms chirp, then ittakes 4 ms to collect data by using all four interrogators.

In some embodiments, the master interrogator module 206 may control theinterrogators 214, 216, 218, and 220 to operate according to a staggeredtrigger schedule. When operated in this manner, the interrogators don'tstart transmitting simultaneously because the transmission start timesare staggered. However, the interrogators do transmit concurrentlyrather than in a one-at-a-time manner as is the case with a round-robinschedule. As one example, master interrogator module 206 may: (1)wirelessly communicate with a specific target device 225 to turn it on;(2) trigger interrogator 214 to transmit an RF signal (e.g., a linearfrequency modulated chirp) to the specific target device and receive aresponsive RF signal from the specific target device; (3) afterinterrogator 214 has started and before it has completed transmitting,trigger interrogator 216 to transmit an RF signal to the specific targetdevice and receive a responsive RF signal from the specific targetdevice; (4) after interrogator 216 has started and before it hascompletes transmitting, trigger interrogator 218 to transmit an RFsignal to the specific target device and receive a responsive RF signalfrom the specific target device; and (5) after interrogator 218 hasstarted and before it completes transmitting, trigger interrogator 220to transmit an RF signal to the target device and receive a responsiveRF signal from the target device. For example, when each interrogatortransmits a 1 ms chirp and the transmission start times are staggered by10 μs (or e.g., any other value in the range of 1-200 μs), all fourinterrogators complete their respective transmissions after 1.04 ms,which is substantially faster than the 4 ms needed for transmission in around-robin implementation.

In some embodiments, only one of the interrogators (e.g., theinterrogator 214 on module 206) may interrogate a target device bytransmitting RF signals to the target device, while all the interrogatordevices (including the transmitting interrogator) may “listen” byreceiving RF signals generated by the target device in response toreceiving RF signals from the transmitting interrogator. So that each ofthe interrogators may correlate the RF signals received from the targetdevice with the RF signal transmitted by the transmitting interrogator,the master interrogator module 206 may control the interrogators 214,216, 218, and 220 to operate in a phase coherent manner. In someembodiments, phase coherence among the interrogators may be achieved byproviding each of the interrogators with a common reference signal(e.g., a clock, a fixed-frequency signal generated by a referenceoscillator, or a direct digitally synthesized reference signal). Aspectsof operating multiple interrogators in a phase-coherent manner arefurther described herein including with reference to FIGS. 14A-D and 17.Phase coherent operation of multiple transmitters may result in thefastest time for obtaining measurements (as compared to the round robinor staggered start schemes described above). For example, when thetransmitting interrogator transmits a 1 ms chirp, all four interrogatorsmay receive the responsive RF signals within 1 ms.

In some embodiments, the timing circuitry 208 may be configured toprovide a clock reference for one or more components of system 200. Forexample, the timing circuitry 208 may be configured to provide a clockreference to control circuitry 210 (which, as described below, may be amicroprocessor). As another example, the timing circuitry 208 may beconfigured to provide a clock reference to interrogator 214 (e.g., to aphased lock loop part of interrogator 214). In some embodiments, thetiming circuitry 208 may comprise a crystal oscillator (e.g., atemperature-controlled crystal oscillator).

In some embodiments, the control circuitry 210 may be configured tomanage operation of the interrogators 214, 216, 218, and 220 inaccordance with any of the schemes described herein. For example, thecontrol circuitry 210 may be configured to manage the interrogators 214,216, 218, and 220 to operate in accordance with a round-robin schedule,a staggered start schedule, or in a phase coherent manner. Inembodiments where the interrogators are operated phase coherently withone another, the control circuitry 210 may be configured to generate acommon reference signal (e.g., a clock, a fixed-frequency signalgenerated by a reference oscillator, or a direct digitally synthesizedreference signal), which common reference signal may then be provided tothe interrogator via one or more wires on the PCB 204. Additionally, thecontrol circuitry 210 may be configured to control, using communicationscircuitry 212, the target device(s) 225 (e.g., by controlling whichtarget devices are on or off at particular times).

In some embodiments, each of the interrogators onboard PCB 204 mayobtain respective information indicative of the distance between theinterrogator and a target device, and provide it to control circuitry210 for processing in furtherance of determining a location of thetarget device. Non-limiting examples of such information, that may beobtained by an interrogator, include an analog mixed RF signal (obtainedby mixing a version an RF signal used to interrogate the target devicewith a responsive RF signal transmitted by the target device), a sampledversion of the analog mixed RF signal, a time-domain waveform obtainedby applying a transform (e.g., an inverse discrete Fourier transform) tothe sampled version of the analog mixed signal, an estimate of the timeof flight between the interrogator and the target device (e.g., obtainedfrom the time-domain waveform), or an estimate of the distance betweenthe interrogator and the target device. Control circuitry 210 may obtainsuch information from each of the interrogators and process the obtainedinformation in order to: (1) obtain estimates of distance between eachof the interrogators and the target device (to the extent that suchestimates are not already provided by the individual interrogatorsthemselves); and (2) determine the target device's location (e.g., thelocation in 3D coordinates) based on the distance estimates.

The control circuitry 210 may obtain any of the above-describedinformation from the interrogators onboard PCB 204 in any suitable way.For example, in some embodiments, information may be transmitted acrossthe PCB 204 using a low-bandwidth analog signal (e.g., using asingle-ended analog line, a shielded line, or a different line pair). Asanother example, in some embodiments, information may be transmittedacross the PCB 204 using digital lines (e.g., when the interrogatorshave built-in analog-to-digital converters). In some embodiments, eachof the interrogators may include double-buffered random access memory(RAM). The double buffered RAM on an interrogator may be read out (toprovide data to the control circuitry 210), while the interrogator isacquiring its next waveform. As such, using double-buffered RAM wouldenable the system 200 to operate at a high rate. The control circuitry210 may be implemented in any suitable way and, for example, may beimplemented as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a combination of logic circuits, amicrocontroller, or a microprocessor.

In some embodiments, some of the processing performed by controlcircuitry 210 may instead be performed on another processor onboard PCB204. For example, the product 202 may include a microprocessor (e.g., asmartphone, a game system, a laptop may each include a microprocessor)and this microprocessor may be used to perform some processing infurtherance of determining the location of a target device instead ofhaving that same processing be performed by the control circuitry 210.For example, in some embodiments, a microprocessor onboard product 202may process distances between a target device 225 and each of theinterrogators 214, 216, 218, and 220 to obtain an estimate of thelocation of the target device 225. Though it should be appreciated thatthe microprocessor onboard product 202 may be configured to perform anyother processing in furtherance of determining the location of thetarget device, as aspects of the technology described herein are notlimited in this respect.

As discussed above, the inventors have recognized that harmonic couplingbetween the transmit antenna and the receive antenna on an interrogatordevice may degrade its performance. In some embodiments, for example, aninterrogator may be configured to transmit, to a target device, RFsignals having a first center frequency, and receive, from the targetdevice, RF signals having a second center frequency that is a harmonicof the first center frequency. While generating RF signals having afirst center frequency, the interrogator may also generate nuisance RFsignals having the second center frequency, for example, because ofnon-linear circuitry components in the signal generation andtransmission chain (e.g., amplifiers, frequency multipliers, etc.).These nuisance RF signals may be detected by the interrogator's receiveantenna (when this occurs the transmit and receive antennas may be saidto be harmonically coupled) and interfere with the ability of theinterrogator's receive antenna to detect RF signals transmitted by thetarget device. As a result, the interrogator may not be able to detectRF signals emitted by the target device unless the target device isphysically close to the interrogator (e.g., within 3 meters or less).Consequently, reducing harmonic coupling may facilitate detecting RFsignals from a target device at greater distances (e.g., 20-40 meters).Reducing harmonic coupling on the transmit and receive antennas of atarget device may also improve the performance of the overall system.

One of the techniques, developed by the inventors, for reducing harmoniccoupling between the transmit antenna and the receive antenna on aninterrogator device includes differentially feeding one or both of thetransmit and receive antennas to differential transmit and/or receivecircuitry on the interrogator device. For example, FIG. 3 shows anillustrative embodiment of interrogator device 102, in which transmitantenna 114 is differentially coupled to transmit and receive circuitry112 via transmission lines 152 a and 152 b. Additionally, receiveantenna 116 is differentially coupled to transmit and receive circuitry112 via transmission lines 154 a and 154 b. Although in the embodimentof FIG. 3, both antennas are differentially coupled to the transmit andreceive circuitry 112, in other embodiments, only one of the twoantennas (either the transmit or the receive antenna) may be coupled tothe transmit and receive circuitry. Similarly, in embodiments where atarget device has a transmit and a receive antenna, one or both of thetransmit and the receive antennas may be differentially coupled to thecircuitry on the target device.

In some embodiments, the interrogator's receive antenna may beconfigured to receive RF signals having a center frequency that is at aneven-order harmonic of the center frequency of the RF signalstransmitted by the interrogator's transmit (e.g., twice the centerfrequency of the transmitted RF signals, four times the center frequencyof the transmitted RF signals, etc.). The inventors have recognized thatusing differential transmission lines from the receive antenna to feeddifferential receive circuitry will also attenuate any common modeinterference from the transmitter. The inventors have also recognizedthat providing RF signals to the transmit antenna (e.g., antenna 112)using differential amplifiers in concert with differential transmissionlines (e.g., lines 152 a and 152 b) will cause the even-order harmonicspresent in the RF signals to cancel, thereby reducing or eliminating thedetection by the interrogator's receive antenna (e.g., antenna 114) ofRF signals generated on the interrogator and having frequencies at theeven-order harmonics. This reduction in interference increases thedistance at which the interrogator's receive antenna can detect RFsignals transmitted by a target device.

As an illustrative example, in some embodiments, the transmit antenna114 may be configured to transmit RF signals having a center frequencyat 61.25 GHz and the receive antenna 116 may be configured to receive RFsignals having a center frequency of 122.5 GHz. By differentiallysignaling the transmit antenna 114 (i.e., by providing RF signals fromtransmit and receive circuitry 112 to transmit antenna 114 viadifferential transmission lines 152 a and 152 b), the amount of RFsignals generated by the interrogator and having a center frequency of122.5 GHz may be reduced or eliminated, thereby reducing or eliminatingthe detection of such signals by the receive antenna 116.

Additionally, differentially signaling the transmit antenna 114 and/orthe receive antenna 116 reduces the sensitivity of the antenna(s) toexternal noise sources and/or common-mode signals, which may cancel outat least partially or fully, when differential transmission lines areused. Accordingly, in some embodiments, at least one (e.g., all)antennas on an interrogator may be differentially coupled to othercircuitry (e.g., circuitry integrated with semiconductor die, which ismounted) on the interrogator. Similarly, in some embodiments, at leastone (e.g., all) antennas on a target device may be differentiallycoupled to circuitry (e.g., circuitry integrated with semiconductor die,which is mounted) on the target device.

Another technique developed by the inventors for reducing the amount ofharmonic coupling between the transmit and receive antennas involvesusing transmit and receive antennas that are polarized differently fromone another. In addition to decreasing harmonic coupling, the manner inwhich the transmit and/or receive antennas are polarized may be used toeffect of background clutter on the received RF signals. Accordingly, insome embodiments, an interrogator's transmit antenna may be configuredto transmit RF signals having a first type of polarization and itsreceive antenna may be configured to receive RF signals having a secondtype of polarization that is different from the first type ofpolarization. In such embodiments, a target device may include a receiveantenna configured to receive, from the interrogator, RF signals havingthe first type of polarization and a transmit antenna configured totransmit RF signals having the second type of polarization.

For example, in some embodiments, the transmit antenna on aninterrogator may be configured to transmit, to a target device, RFsignals circularly polarized in a first rotational direction and thereceive antenna on the interrogator may be configured to receive, fromthe target device, RF signals circularly polarized in a secondrotational direction different from the first rotational direction.Complementarily, the receive antenna on the target device may beconfigured to receive, from the interrogator, RF signals circularlypolarized in the first rotational direction, and the transmit antenna onthe target device may be configured to transmit RF signals circularlypolarized in the second rotational direction.

Circularly polarized RF signals may be referred to as havingright-handed circular polarization (RHCP) or left-handed circularpolarization (LHCP) depending on the direction in which the electricfield rotates from the perspective of the source.² Accordingly, acircularly polarized RF signal has right-handed circular polarizationwhen, upon pointing the right thumb away from the source in the samedirection that the circularly polarized signal is propagating, theelectric filed rotates in the direction of the curled fingers of theright hand. Right-handed circular polarization may also be referred toas “clockwise” circular polarization. Right-handed circular polarizationis illustrated in FIG. 4B, which shows how the direction of the electricfield rotates along the direction of propagation for an electromagneticsignal having RHCP (the source may be considered to be at the originwhere the three depicted axes intersect). On the other hand, acircularly polarized RF signal has left-handed circular polarizationwhen, upon pointing the left thumb away from the source in the samedirection that the circularly polarized signal is propagating, theelectric filed rotates in the direction of the curled fingers of theleft hand. Left-handed circular polarization may also be referred to as“counter-clockwise” circular polarization. Left-handed circularpolarization is illustrated in FIG. 4A, which shows how the direction ofthe electric field rotates along the direction of propagation for anelectromagnetic signal having LHCP. As may be appreciated from theforegoing, RF signals having right-handed (or clockwise) circularpolarization and RF signals having left-handed (or counter-clockwise)circular polarization are circularly polarized in different and opposingdirections. ² Although it is possible to define right- andleft-handedness from the perspective of the target rather than thesource, we do not adopt this convention here.

Continuing the above example, in some embodiments, the transmit antennaof an interrogator device may be configured to transmit, to a targetdevice, RF signals having right-handed circular polarization(hereinafter, “RHCP” RF signals) and the receive antenna of theinterrogator device may be configured to receive, from the targetdevice, RF signals having left-handed circular polarization(hereinafter, “LHCP” RF signals). Complementarily, the receive antennaof the target device may be configured to receive, from the interrogatordevice, RHCP RF signals and the transmit antenna of the target devicemay be configured to transmit LHCP RF signals. In other embodiments, theconfiguration may be reversed so that the transmit antenna of aninterrogator device may be configured to transmit, to a target device,LHCP RF signals and the receive antenna of the interrogator device maybe configured to receive, from the target device, RHCP RF signals.Complementarily, the receive antenna of the target device may beconfigured to receive, from the interrogator device, LHCP RF signals andthe transmit antenna of the target device may be configured to transmitRHCP RF signals.

FIG. 16 is a flowchart of an illustrative process 1600 for makingdistance measurements using an interrogator device configured totransmit, to at least one target device, RF signals circularly polarizedin one rotational direction and receive, from the at least one targetdevice, RF signals circularly polarized in another rotational direction,in accordance with some embodiments of the technology described herein.The process 1600 may be performed by any suitable type of interrogatordevice described herein that has transmit and receive antennasconfigured to transmit and receive RF signals having using differentpolarizations and any suitable type of target device described hereinthat has transmit and receive antennas configured to receive andtransmit RF signals having different polarizations.

Process 1600 begins at act 1602, where a transmit antenna on aninterrogator device, transmits, to a target device, a first RF signalcircularly polarized in a first rotational direction. In someembodiments, the first RF signal may be an RHCP RF signal (havingclockwise circular polarization). In other embodiments, however, thefirst RF signal may be a LHCP RF signal (having counter-clockwisecircular polarization).

The interrogator's transmit antenna may be any suitable type of antennaconfigured to transmit circularly polarized signals. The transmitantenna may be directional or isotropic. In some embodiments, thetransmit antenna may be a circularly polarized antenna fabricated on asubstrate. For example, the circularly polarized antenna may be a patchantenna, a planar spiral antenna, an antenna comprising a first linearlypolarized antenna and a second linearly polarized antenna disposedorthogonally to the first linearly polarized antenna.

Next, process 1600 proceeds to act 1604, where a receive antenna on thetarget device receives, from the interrogator a second RF signalcircularly polarized in the first rotational direction. The second RFsignal received by the target device at act 1604 may correspond to(e.g., may be the received version of) the first RF signal transmittedby the interrogator at act 1602. For example, when the interrogatortransmit antenna transmits a first RHCP RF signal at act 1602, thereceive antenna on the target device may receive a second RHCP RF signalcorresponding to the first RHCP signal at act 1604. As another example,when the interrogator transmit antenna transmits a first LHCP RF signalat act 1602, the receive antenna on the target device may receive asecond LHCP RF corresponding to the first LHCP signal at act 1604.Although the first and second RF signals may be the same, they need notbe, at least because the first RF signal may be altered (e.g., theamplitude, phase, and/or frequency of the RF signal may be altered) asit propagates from the interrogator to the target device.

The target device receive antenna may be any suitable type of antennaconfigured to receive circularly polarized signals. It may bedirectional or isotropic. In some embodiments, the receive antenna maybe a circularly polarized antenna fabricated on a substrate (e.g., apatch antenna, a planar spiral antenna, an antenna comprising a firstlinearly polarized antenna and a second linearly polarized antennadisposed orthogonally to the first linearly polarized antenna).

Next, process 1600 proceeds to act 1606, where a transmit antenna on thetarget device transmits, to the interrogator, a third RF signalcircularly polarized in a second rotational direction different from(e.g., opposite of) the first rotational direction. For example, whenthe receive antenna on the target device is configured to receive RHCPRF signals, the transmit antenna on the target device is configured totransmit LHCP RF signals or vice versa.

In some embodiment, the target device may generate the third RF signalbased on the second RF signal. For example, after receiving the secondRF signal polarized in the first rotational direction (e.g., clockwisedirection) at act 1604, the target device may process the second RFsignal (e.g., by passing it through one or more amplifiers, one or morefrequency multipliers, mixing the second RF signal with one or moreother RF signals, and/or performing any of the processing describedherein with respect to any target device), and provide the processedsecond RF signal to the transmit antenna which is configured to transmitRF signals polarized in the second rotational direction (e.g.,counter-clockwise direction). In this way, the transmit antenna on thetarget device is driven by the processed second RF signal to transmit athird RF signal polarized in the second rotational direction.

The target device transmit antenna may be any suitable type of antennaconfigured to transmit circularly polarized signals. It may bedirectional or isotropic. The transmit antenna may be a circularlypolarized antenna fabricated on a substrate (e.g., a patch antenna, aplanar spiral antenna, an antenna comprising a first linearly polarizedantenna and a second linearly polarized antenna disposed orthogonally tothe first linearly polarized antenna).

Next, process 1600 proceeds to act 1608, where a receive antenna on theinterrogator receives a fourth RF signal circularly polarized in thesecond rotational direction. The fourth RF signal received by theinterrogator at act 1608 may correspond to (e.g., may be the receivedversion of) the third RF signal transmitted by the target device at act1606. For example, when the transmit antenna on the target devicetransmits a third RHCP RF signal at act 1606, the receive antenna on theinterrogator may receive a corresponding fourth RHCP RF signal at act1608. As another example, when the transmit antenna on the target devicetransmits a third LHCP RF signal at act 1606, the receive antenna on thetarget device may receive a corresponding fourth LHCP RF signal at act1608. Although the third and fourth RF signals may be the same, theyneed not be, at least because the third RF signal may be altered (e.g.,the amplitude, phase, and/or frequency of the third RF signal may bealtered) as it propagates from the target device to the interrogator.

The interrogator receive antenna may be any suitable type of antennaconfigured to receive circularly polarized signals. The receive antennamay be directional or isotropic. The receive antenna may be a circularlypolarized antenna fabricated on a substrate (e.g., a patch antenna, aplanar spiral antenna, an antenna comprising a first linearly polarizedantenna and a second linearly polarized antenna disposed orthogonally tothe first linearly polarized antenna).

After the fourth RF signal is received by the interrogator, the fourthRF signal may be processed in any suitable way in furtherance ofdetermining a distance between the interrogator and the target device.For example, the fourth RF signal may be processed by the circuitry inthe interrogator in accordance with any of the ways described hereinincluding with reference to FIGS. 8A-8D and 11A-11B. In someembodiments, for example, the fourth RF signal may be mixed with afrequency-multiplied version of first RF signal to produce a mixed RFsignal, which mixed RF signal may be used to determine the distancebetween the interrogator and the target device. It should beappreciated, however, that the fourth RF signal is not limited to beingused solely for determining the distance between the interrogator andthe target device and may be used for any other suitable purpose, asaspects of the technology described herein are not limited in thisrespect.

As discussed above, the inventors recognized the benefits of developingrelatively low cost, small footprint micro-localization componentsafforded by chip-scale technologies. Unlike conventional designs thatare typically too complex for chip-scale production, the designsdeveloped by the inventors facilitate the ability to manufacturecomponents of a micro-localization system using semiconductorfabrication processes. According to some embodiments, interrogatordevices and target devices are manufactured as chip-scale products, someexamples of which are described in further detail below.

FIG. 5A is a block diagram of an illustrative embodiment of aninterrogator device 500 that may be used as part of process 1600 (e.g.,to perform acts 1602 and 1608 of process 1600). Interrogator device 500is not limited to being used as part of process 1600 and may be used inany other suitable way, including as part of any other process describedherein, as aspects of the technology described herein are not limited inthis respect.

As shown in FIG. 5A, interrogator 500 comprises a substrate 505 having adifferential feed circular polarized transmit antenna 502 and adifferential feed circular polarized receive antenna 506 disposedthereon. The interrogator 500 further comprises semiconductor die 504having transmit and receive circuitry integrated thereon. The transmitand receive circuitry integrated with the semiconductor die 504 isdifferentially coupled to antenna 502 via lines 507 a and 507 b. Thetransmit and receive circuitry on the semiconductor die is alsodifferentially coupled to antenna 506 via lines 508 a and 508 b.

In some embodiments, the substrate 505 may provide a means forimplementing low-cost RF transmit and/or receive antennas (e.g.,antennas 502 and 506) located near a semiconductor die (e.g., die 504)having circuitry for providing RF signals for transmission by thetransmit RF antenna and circuitry for obtaining and processing RFsignals received by the receive antenna. The substrate 505 may comprisea printed circuit board (PCB) and/or be manufactured from any suitableprinted circuit board materials or other materials capable of supportingpropagation of RF signals in a desired range of frequencies. Forexample, substrate 505 may be manufactured from materials that supportpropagation of microwave and/or millimeter wave RF signals. As oneillustrative example, substrate 505 may be manufactured from materialsthat support propagation of microwave signals having frequencies in therange of 0.5-20 GHz, 4-6 GHz, 8-12 GHz, 50-70 GHz, 100-140 GHz, 50GHz-240 GHz, and/or any suitable frequency range within the unioncombination of such ranges.

In some embodiments, the substrate 505 may include one or more layersand/or coatings for reducing the harmonic coupling between the transmitand receive antennas on the substrate. For example, the substrate 505may include a frequency selective surface (FSS) configured to reduceharmonic coupling between the transmit antenna 502 and the receiveantenna 506. The FSS may be manufactured as one or more layers withinand/or on top of the substrate 505. The FSS may be of any suitable typeand, for example, may comprise a periodic array of (e.g., metallic)elements on a dielectric substrate.

In some embodiments, the FSS may attenuate undesired RF signalstraveling across the substrate 505 between the two antennas 502 and 506.The FSS may attenuate undesired RF signals by blocking their propagationacross the substrate and reflecting them back toward the transmitantenna. For example, the FSS may attenuate RF signals, traveling acrosssubstrate 505 from transmit antenna 502 to receive antenna 506, having acenter frequency at a harmonic (e.g., 122.5 GHz) of the center frequency(e.g., 61.25 GHz) of signals being transmitted by antenna 502.Additionally or alternatively, the FSS may attenuate coupling RF signalstraveling between the differential lines 507 a and 507 b, between thedifferential lines 508 a and 508 b, and/or between ports of the die 508.

Accordingly, in some embodiments, the FSS on substrate 505 may be tunedto blocking RF signals having a particular frequency or set offrequencies. For example, the FSS may be tuned to block RF signalshaving frequencies (e.g., 122.5 GHz) that the receive antenna 506 isconfigured to receive from one or more target devices. Additionally oralternatively, the FSS may be tuned to block RF signals havingfrequencies (e.g., 61.25 GHz) that the transmit antenna 502 isconfigured to transmit (e.g., to prevent the transmitter frompotentially saturating the low-noise amplifier configured to amplifysignals received by the receive antenna 506).

In addition to or instead of using a frequency-selective surface, insome embodiments, the substrate 505 may be coated with an absorbentcoating configured to reduce harmonic coupling between the transmitantenna 502 and the receive antenna 506. The absorbent coating may beconfigured to absorb any incident microwaves and dissipate them as heatenergy. Any suitable absorbent coating may be used. For example, theabsorbent coating may comprise carbon material such as, for example,resistive card or sheet stock material or carbon impregnated foam.

In some embodiments, each of differential feed circular polarizedantennas 502 and 506 may be fabricated on the substrate 505. Forexample, substrate 505 may comprise one or more conductive layers andeach of antennas 502 and 506 may be fabricated on the substrate 502 atleast in part by patterning the conductive layer(s). Each of antennas502 and 506 may be a planar spiral antenna, a patch antenna (e.g., atruncated patch antenna as shown in FIG. 6A), an antenna comprising twolinearly polarized antenna disposed perpendicularly to one another, aMEMS antenna, a dipole antenna, or any other suitable type of antenna.

In some embodiments, the antennas 502 and 506 may be directionalantennas having a higher power aperture than isotropic antennas, whichmay allow the antennas to focus the transmission and/or receipt of RFsignals to/from a particular direction (e.g., in a direction where oneor more target devices of interest may be located). In some embodiments,however, one or both of antennas 502 and 506 may be isotropic antennas,as aspects of the technology described herein are not limited in thisrespect.

In some embodiments, antenna 502 may be configured to transmit RFsignals circularly polarized in a first rotational direction (e.g.,clockwise) and the antenna 506 may be configured to receive RF signalscircularly polarized RF in a second rotational direction different fromthe first rotational direction (e.g., counter-clockwise). In otherembodiments, however, each of antenna 502 and 506 may be configured totransmit and receive RF signals circularly polarized in the samerotational direction. For example, both antennas 502 and 506 may beconfigured to receive and transmit RF signals having clockwise circularpolarization. As another example, both antennas 502 and 506 may beconfigured to receive and transmit RF signals having counter-clockwisecircular polarization.

In some embodiments, antenna 502 may be configured to transmit RFsignals having a first center frequency and the antenna 506 may beconfigured to receive RF signals having a second center frequencydifferent from the first center frequency. For example, the secondcenter frequency may be greater than a harmonic of the first centerfrequency (e.g., a first harmonic of the first center frequency, whichis twice the first frequency). As one illustrative example, the antenna502 may be configured to transmit RF signals having a first centerfrequency in the range of 50-70 GHz (e.g., 61.25 GHz), and the antenna506 may be configured to receive RF signals having a second centerfrequency in the range of 100-140 GHz (e.g., 122.5 GHz). As anotherillustrative example, the antenna 502 may be configured to transmit RFsignals having a first center frequency in a range of 4-6 GHz (e.g., 5GHz), and the antenna 506 may be configured to receive RF signals havinga second center frequency in a range of 8-10 GHz. In some embodiments,antenna 502 may be a different size from antenna 506. For example,antenna 502 may have a larger area than antenna 506 in embodiments wherethe antenna 506 is configured to receive RF signals having a centerfrequency (e.g., 122.5 GHz) greater than the center frequency of thesignals transmitted by antenna 502 (e.g., 61.25 GHz).

The semiconductor die 504 may be a silicon die, for instance from a bulksilicon wafer or silicon-on-insulator (SOI) wafer. In some embodiments,the semiconductor die 504 may be a single crystal silicon die. In someembodiments, the semiconductor die 504 may be a CMOS die, a BiCMOS die,a GaAs die, a GaN die, or may be formed of any other suitablesemiconductor material. In some embodiments, the semiconductor die 504may be flip-chip bonded to substrate 505. In other embodiments, thesemiconductor die 504 may be wire bonded to the substrate 505 or mountedon substrate 505 in any other suitable way.

In some embodiments, the interrogator 500 may comprise circuitryintegrated with semiconductor die 504 and configured to provide RFsignals to the transmit antenna 502 and receive RF signals from thereceive antenna 506. The circuitry may comprise circuitry used forgenerating RF signals to transmit via antenna 502 (e.g., a waveformgenerator, one or more amplifiers, etc.), circuitry for performing phasecoherent processing of received RF waveforms (e.g., circuitry tomultiply the frequencies in a copy of the transmitted RF signal to thefrequencies in a received RF signal, a frequency mixer for mixing atransformed version of the transmitted RF signal and the received RFsignals), and/or any other suitable circuitry, numerous examples ofwhich are provided herein including with reference to FIGS. 8A-8D and11A-11B.

In the illustrated embodiment, the circuitry integrated with die 504 isdifferentially coupled to antenna 502 via lines 508 a and 508 b. Thecircuitry may generate a first signal and a second signal out of phase(e.g., 180 degrees out of phase) with the first signal, and concurrentlyprovide the first and second signals to the antenna 502 via lines 508 aand 508 b, respectively. In turn, antenna 502 may be configured totransmit a signal based on a difference between the first and secondsignals. Additionally, the circuitry integrated with die 504 isdifferentially coupled to antenna 506 via lines 509 a and 509 b. Theantenna 506 is configured to receive an RF signal and transmit itthrough the differential pair of lines 509 a and 509 b.

FIG. 5B is a block diagram illustrating components of an exampledual-mode localization device 520 configured to operate as aninterrogator or as a transponder. Dual-mode localization device 520comprises a substrate 522 having four antennas disposed thereon. Theseantennas include interrogator transmit antenna 524, interrogator receiveantenna 526, target device transmit antenna 528, and target devicereceive antenna 530. The localization device 520 further comprises asemiconductor die 532 mounted on substrate 522. The semiconductor die532 has interrogator circuitry 534 and target device circuitry 536integrated thereon.

As shown in FIG. 5B, interrogator transmit antenna 524 is differentiallycoupled to interrogator circuitry 534 via transmission lines 525 a and525 b, and interrogator receive antenna is differentially coupled tointerrogator circuitry 534 via transmission lines 527 a and 527 b.Target device transmit antenna 528 is differentially coupled to targetdevice circuitry 536 via transmission lines 529 a and 529 b. Targetdevice receive antenna 530 is differentially coupled to target devicecircuitry 536 via transmission lines 531 a and 531 b. Though in theillustrative embodiment of FIG. 5B each of the antennas 524, 526, 528,and 530 is differentially coupled to circuitry on the semiconductor die532, in other embodiments one or more of these antennas may not bedifferentially coupled to the circuitry.

Substrate 522 may be of any suitable type described herein includingwith reference to substrate 505 of FIG. 5A and, for example, maycomprise a printed circuit board (PCB) and/or be manufactured from anysuitable printed circuit board materials or other materials capable ofsupporting propagation of RF signals in a desired range of frequencies.In some embodiments, the substrate 522 may include a frequency selectivesurface and/or absorbent coating to reduce harmonic coupling among theantennas in device 522 (e.g., reduce harmonic coupling between theinterrogator transmit antenna 524 and the interrogator receive antenna526 and/or reduce harmonic coupling between the target device transmitantenna 528 and the target device receive antenna 530).

In some embodiments, each of antennas 524, 526, 528, and 530 may befabricated on substrate 522. For example, substrate 522 may comprise oneor more conductive layers and each of the antennas 524, 526, 528, and530 may be fabricated on the substrate 522 at least in part bypatterning the conductive layer(s). Each of antennas 524, 526, 528, and530 may be a planar spiral antenna, a patch antenna, an antennacomprising two linearly polarized antenna disposed perpendicularly toone another, a MEMS antenna, a dipole antenna, or any other type ofantenna.

Antennas may be patterned on the substrate 522 in any suitable manner toproduce a conductive pattern, for example, using any one or combinationof various subtractive, additive and/or semi-additive processes.Subtractive processes selectively remove conductive material (e.g.,copper) from a conductive layer of the substrate leaving a desiredconductive pattern using, for example, any of various lithographicprocesses including, but not limited to, chemical etching,photoengraving, etc. Such processes are typically performed by providinga resist material in the desired pattern (often referred to as a mask)and introducing the conductive layer to the corresponding etchant toremove the conductive material in locations not treated with the resistmaterial. Another subtractive process involves milling away unwantedportions of the conductive layer leaving the desired conductive pattern.

Additive processes may also be used and may involve electroplating thedesired conductive pattern on the substrate or “printing” the patternusing a conductive ink. For example, electroplating may involve exposingphotosensitive film masked in a desired pattern. The exposed pattern maythen be introduced to a chemical bath to allow the pattern to be capableof metal ion bonding and then plated with a conductor (e.g., withcopper) that bonds with the pattern sensitized in the chemical bath toform the desired conductive pattern. Additive processes have theadvantage that less conductive material is needed to form the desiredconductive pattern than subtractive techniques. Other processes combineboth subtractive and additive techniques to form the desired conductivepattern. It should be appreciated that any suitable fabrication processmay be used to pattern desired antennas on substrate 522, as the aspectsare not limited in this respect. Indeed, the subtractive processesdescribed herein, additive processes described herein, and/or any othersuitable process may be used alone or in any combination to fabricatethe desired conductive pattern for the antennas (e.g., antennas 524,526, 528, and 530, antennas 502 and 506 described with reference to FIG.5A, antennas 114 and 116 described with reference to FIG. 1B, and/or anyother antennas described herein).

In some embodiments, interrogator transmit antenna 524 may be configuredto transmit RF signals circularly polarized in a first rotationaldirection (e.g., clockwise) and the interrogator receive antenna 526 maybe configured to receive RF signals circularly polarized RF in a secondrotational direction different from the first rotational direction(e.g., counter-clockwise). Additionally, in some embodiments, the targetdevice receive antenna 528 may be configured to receive RF signalcircularly polarized in the first rotational direction and the targetdevice transmit antenna 530 may be configured to transmit RF signalscircularly polarized in the second rotational direction. Accordingly, insome embodiments, the interrogator transmit antenna 524 and the targetdevice receive antenna 530 may be configured to transmit/receive RFsignals circularly polarized in the same direction. Likewise, targetdevice transmit antenna 528 and interrogator receive antenna 526 may beconfigured to transmit/receive RF signals circularly polarized in thesame direction.

In some embodiments, when dual mode device 520 is operating as aninterrogator (in an “interrogator mode”), the interrogator transmitantenna 524 may be configured to transmit RF signals having a firstcenter frequency and the interrogator receive antenna 526 may beconfigured to receive RF signals having a second center frequencydifferent from (e.g., a harmonic of) the first center frequency.Examples of such first and second center frequencies are providedherein. When dual mode device 520 is operating as a target device (in a“target device mode”), the target device receive antenna 530 may beconfigured to receive RF signals having the first center frequency andthe target device transmit antenna 528 may be configured to transmit RFsignals having the second center frequency. Accordingly, in someembodiments, the interrogator transmit antenna 524 and the target devicereceive antenna 530 may be configured to transmit/receive RF signalshaving the same center frequency (e.g., 60 GHz). Likewise, target devicetransmit antenna 528 and interrogator receive antenna 526 may beconfigured to transmit/receive RF signals having the same centerfrequency.

The semiconductor die 532 may be a silicon die, for instance from a bulksilicon wafer or silicon-on-insulator (SOI) wafer. In some embodiments,the semiconductor die 532 may be a single crystal silicon die. In someembodiments, the semiconductor die 532 may be a CMOS die, a BiCMOS die,a GaAs die, a GaN die, or may be formed of any other suitablesemiconductor material. In some embodiments, the semiconductor die 532may be flip-chip bonded to substrate 522. In other embodiments, thesemiconductor die 532 may be wire bonded to the substrate 522 or mountedon substrate 522 in any other suitable way.

In some embodiments, interrogator circuitry 534 may be configured toprovide RF signals to the interrogator transmit antenna 524 and receiveRF signals from the interrogator receive antenna 526. Interrogatorcircuitry 534 may be implemented in any suitable way described hereinincluding in any of the ways described with reference to FIGS. 8A-8D and11A-11B. In some embodiments, target device circuitry 536 may beconfigured to receive RF signals from the target device receive antenna530 and to provide RF signals to the target device transmit antenna 528.Target device circuitry 536 may be implemented in any suitable waydescribe herein including in any of the ways described herein withreference to FIGS. 9A-9H, 10, and 11A-11B.

FIG. 6A is a block diagram illustrating components of an exampleinterrogator device 600, in accordance with some embodiments of thetechnology described herein. The interrogator device 600 is illustratedalong with dimensions of some of the components thereon to provide asense of scale of the device and the components. It should beappreciated that these dimensions are illustrative of the exampleembodiment of FIG. 6A, but do not limit the dimensions of theinterrogator device and/or its components in other embodiments.

As shown in FIG. 6A, interrogator 600 comprises a substrate 602 having adifferentially feed circular polarized transmit antenna 604 and adifferential feed circular polarized receive antenna 606 disposedthereon. The interrogator 600 further comprises semiconductor die 608having transmit and receive circuitry integrated thereon. The transmitand receive circuitry integrated with the semiconductor die 608 isdifferentially coupled to antenna 602 via lines 609 a and 609 b. Thetransmit and receive circuitry on the semiconductor die is alsodifferentially coupled to antenna 606 via lines 610 a and 610 b.

Substrate 602 may be of any suitable type described herein includingwith reference to substrate 505 of FIG. 5A and, for example, maycomprise a printed circuit board (PCB) and/or be manufactured from anysuitable printed circuit board materials or other materials capable ofsupporting propagation of RF signals in a desired range of frequencies.In some embodiments, the substrate 602 may include a frequency selectivesurface and/or absorbent coating to reduce harmonic coupling between thetransmit antenna 604 and the receive antenna 606. Examples of frequencyselective surfaces and absorbent coatings are described herein. In theillustrative embodiment of FIG. 6A, the substrate 602 may be 4 mm×5 mm.

In the illustrative embodiment of FIG. 6A, transmit antenna 604 is apatch antenna configured to transmit circularly polarized RF signalshaving a center frequency of 61.25 GHz. The RF signals may be circularlypolarized clockwise or counter-clockwise. Although the antennas 604 and606 are patch antennas in the illustrative embodiment of FIG. 6A, inother embodiments, each of the antennas 604 and 606 may be of any othersuitable type including any of the types described herein. Additionally,although the antennas 604 and 606 transmit/receive RF signals at 61.25GHz/122.5 GHz in the illustrative embodiment of FIG. 6A, these antennasmay be configured to transmit/receive at any other suitable (e.g.,millimeter wave and/or microwave) frequencies f₀/kf₀, where the transmitantenna 604 is configured to transmit RF signals having a centerfrequency of f₀ and the receive antenna 606 is configured to receive RFsignals having a center frequency of kf₀, which is a harmonic of f₀. Inthe illustrative embodiment of FIG. 6A, the transmit antenna 604 is a2.5 mm×2.1 mm patch antenna and the receive antenna is a 1.25 mm by 0.86mm patch antenna.

In some embodiments, each of antennas 604 and 606 may be fabricated onsubstrate 602. For example, substrate 602 may comprise one or moreconductive layers and each of antennas 604 and 606 may be fabricated onthe substrate 602 at least in part by patterning the conductivelayer(s). In some embodiments, antenna 604 may be configured to transmitRF signals circularly polarized in a first rotational direction (e.g.,clockwise) and the antenna 606 may be configured to receive RF signalscircularly polarized RF in a second rotational direction different fromthe first rotational direction (e.g., counter-clockwise). In otherembodiments, however, each of antennas 604 and 606 may be configured totransmit and receive RF signals circularly polarized in the samerotational direction.

In some embodiments, the semiconductor die 608 may be a silicon die, forinstance from a bulk silicon wafer or silicon-on-insulator (SOI) wafer.In some embodiments, the die 608 may be a single crystal silicon die. Insome embodiments, the die 608 may be a CMOS die, a BiCMOS die, a GaAsdie, a GaN die, or may be formed of any other suitable semiconductormaterial. In the illustrated embodiment, the die 608 is flip-chip bondedto substrate 602. In other embodiments, the die 608 may be wire bondedto the substrate 602 or mounted on substrate 602 in any other suitableway. In the illustrative embodiment of FIG. 6A, the semiconductor die608 may be 1 mm by 1 mm.

In some embodiments, the interrogator 600 may comprise circuitryintegrated with semiconductor die 608 and configured to provide RFsignals to the transmit antenna 604 and receive RF signals from thereceive antenna 606. The circuitry may comprise circuitry used forgenerating RF signals to transmit via antenna 604 (e.g., a waveformgenerator, one or more amplifiers, etc.), circuitry for performing phasecoherent processing of received RF waveforms (e.g., circuitry tomultiply the frequencies in a copy of the transmitted RF signal to thefrequencies in a received RF signal, a frequency mixer for mixing atransformed version of the transmitted RF signal and the received RFsignals), and/or any other suitable circuitry, numerous examples ofwhich are provided herein including with reference to FIGS. 8A-8D and11A-11B.

In the illustrated embodiment, the circuitry integrated with die 608 isdifferentially coupled to antenna 604 via lines 609 a and 609 b. Thecircuitry may generate a first signal and a second signal out of phase(e.g., 180 degrees out of phase) with the first signal, and concurrentlyprovide the first and second signals to the antenna 604 via lines 609 aand 609 b, respectively. In turn, antenna 604 may be configured totransmit a signal based on a difference between the first and secondsignals. Additionally, the circuitry integrated with die 608 isdifferentially coupled to antenna 606 via lines 610 a and 610 b. Theantenna 606 is configured to receive an RF signal and transmit itthrough the differential pair of lines 610 a and 610 b.

FIG. 6B is a block diagram illustrating components of an example targetdevice 650, in accordance with some embodiments of the technologydescribed herein. The target device 650 is illustrated along withdimensions of some of the components thereon to provide a sense of scaleof the device and the components. It should be appreciated that thesedimensions are illustrative of the example embodiment of FIG. 6B, but donot limit the dimensions of the interrogator device and/or itscomponents in other embodiments.

As shown in FIG. 6B, target device 650 comprises a substrate 652 havinga receive antenna 654 and transmit antenna 656 disposed thereon. Thetarget device 650 further comprises a semiconductor die 658 havingsignal transformation circuitry integrated thereon. The signaltransformation circuitry integrated with the semiconductor die 658 isdifferentially coupled to antenna receive 654 via lines 659 a and 659 b.The signal transformation circuitry on the semiconductor die 658 isdifferentially coupled to transmit antenna 656 via lines 660 a and 660b.

Substrate 652 may be of any suitable type described herein includingwith reference to substrate 505 of FIG. 5A and, for example, maycomprise a printed circuit board (PCB) and/or be manufactured from anysuitable printed circuit board materials or other materials capable ofsupporting propagation of RF signals in a desired range of frequencies.In some embodiments, the substrate 652 may include a frequency selectivesurface and/or absorbent coating to reduce harmonic coupling between thereceive antenna 654 and the transmit antenna 656. Examples of frequencyselective surfaces and absorbent coatings are described herein. In theillustrative embodiment of FIG. 6B, the substrate 652 may be 4 mm×3.5mm.

In the illustrative embodiment of FIG. 6B, receive antenna 654 is afolded dipole antenna configured to receive (e.g., from interrogator600) RF signals having a center frequency of 61.25 GHz. The RF signalsmay be circularly polarized clockwise or counter-clockwise, in someembodiments. Although the antennas 654 and 656 are folded dipoleantennas in the illustrative embodiment of FIG. 6B, in otherembodiments, each of the antennas 654 and 656 may be of any othersuitable type including any of the types described herein. Additionally,although the antennas 654 and 656 receive/transmit RF signals at 61.25GHz/122.5 GHz in the illustrative embodiment of FIG. 6B, these antennasmay be configured to receive/transmit at any other suitable (e.g.,millimeter wave and/or microwave) frequencies f₀/kf₀, where the receiveantenna 654 is configured to receive RF signals having a centerfrequency of f₀ and the transmit antenna 656 is configured to transmitRF signals having a center frequency of kf₀, which is a harmonic of f₀.In the illustrative embodiment of FIG. 6B, the receive antenna 654 is a2.5 mm wide folded dipole antenna and the transmit antenna 656 is a 1.25mm wide folded dipole antenna.

In some embodiments, each of antennas 654 and 656 may be fabricated onsubstrate 652. For example, substrate 652 may comprise one or moreconductive layers and each of antennas 654 and 656 may be fabricated onthe substrate 652 at least in part by patterning the conductivelayer(s). In some embodiments, antenna 654 may be configured to receiveRF signals circularly polarized in a first rotational direction (e.g.,clockwise) and the antenna 656 may be configured to transmit RF signalscircularly polarized RF in a second rotational direction different fromthe first rotational direction (e.g., counter-clockwise). In otherembodiments, however, each of antennas 654 and 656 may be configured totransmit and receive RF signals circularly polarized in the samerotational direction.

In some embodiments, the semiconductor die 658 may be a silicon die, forinstance from a bulk silicon wafer or silicon-on-insulator (SOI) wafer.In some embodiments, the die 658 may be a single crystal silicon die. Insome embodiments, the die 658 may be a CMOS die, a BiCMOS die, a GaAsdie, a GaN die, or may be formed of any other suitable semiconductormaterial. In the illustrated embodiment, the die 658 is flip-chip bondedto substrate 602. In other embodiments, the die 658 may be wire bondedto the substrate 652 or mounted on substrate 652 in any other suitableway. In the illustrative embodiment of FIG. 6B, the semiconductor die658 may be 1 mm by 1 mm.

In some embodiments, the target device 650 may comprise signaltransformation circuitry integrated with semiconductor die 658 andconfigured to receive RF signals from receive antenna 654, transform thereceived RF signals to obtain transformed RF signals, and provide thetransformed RF signals to transmit antenna 656. The signaltransformation circuitry may be configured to transform the received RFsignals by changing the frequencies in the received RF signals in anysuitable way including in any of the ways described herein includingwith reference to FIGS. 9A-9H, 10, 11A, and 11B. For example, the signaltransformation circuitry may be configured to transform the received RFsignals by passing the received RF signals through one or more frequencymultipliers so that received RF signals having a first center frequencyare transformed into RF signals having a second center frequency that isa harmonic of the center frequency. To this end, the signaltransformation circuitry may comprise one or more frequency multipliers,one or more amplifiers, and/or any other suitable components. Variousexamples of signal transformation circuitry are provided hereinincluding with reference to FIGS. 9A-9H, 10, 11A, and 11B.

In the illustrated embodiment, the signal transformation circuitryintegrated with die 658 is differentially coupled to receive antenna 654via lines 659 a and 659 b. The antenna 654 is configured to receive anRF signal and transmit it, via differential signaling, through thedifferential pair of lines 659 a and 659 b. The signal transformationcircuitry may process the received RF signals and generate correspondingtransformed RF signals, which are provided, using differential signalingvia differential lines 660 a and 660 b. The circuitry may generate afirst signal and a second signal out of phase (e.g., 180 degrees out ofphase) with the first signal, and concurrently provide the first andsecond signals to the antenna 654 via lines 659 a and 659 b,respectively. In turn, antenna 656 may be configured to transmit asignal based on a difference between the first and second signals.

As described above, in some embodiments, an interrogator device maycomprise a substrate having one or more antennas fabricated thereon, asemiconductor die flip-chip bonded to the substrate, and circuitryintegrated with the semiconductor die and coupled to the antenna(s)fabricated on the substrate. Similarly, a target device may comprise asubstrate having one or more antennas fabricated thereon, asemiconductor die flip-chip bonded to the substrate, and circuitryintegrated with the semiconductor die and coupled to the antenna(s)fabricated on the substrate. Aspects of techniques for manufacturingsuch interrogator and target devices are described with reference toFIGS. 7A-7F below, which describe aspects of techniques for generating apackaged device having a substrate, a semiconductor die, andencapsulation. The packaged device is described generically with respectto FIGS. 7A-7F, but may be an interrogator device or a target device, insome embodiments.

FIG. 7A is a diagram of an illustrative substrate 700 having a transmitantenna 704 and a receive antenna 706 fabricated thereon. Substrate 700further includes bond pads 708, which are configured to be mated withsemiconductor, die bumps, as described below with reference to FIG. 7Band FIG. 7C. The substrate 700 further comprises second levelconnections 710 to facilitate connecting the device to any suitableother system (e.g., the printed circuit board 204 of product 202 shownin FIG. 2 or the system level or mother board of any other suitablesystem). Second level connections 710 may be a ball grid array (BGA) tofacilitate surface mounting the device to the next level ofinterconnection. Second level connections 710 may also be through-holepins, gull-wing connections or any other suitable second levelconnections.

It should be appreciated that although only four bond pads 708 (lands)are shown in FIG. 7, that is for clarity of presentation and not by wayof limitation, as substrate 700 may comprise any suitable number of bondpads 708. For example, substrate 700 may comprise anywhere between 10and 150 bond pads. As one illustrative example, when substrate 700 isused to implement an interrogator device, the substrate 700 may include10-35 (e.g., 25) bond pads. As another illustrative example, whensubstrate 700 is used to implement a target device, the substrate 700may include 50-75 (e.g., 64) bond pads. As yet another illustrativeexample, when substrate 700 is used implement a combined interrogatorand target device, the substrate 700 may include 60-110 bond pads.

Substrate 700 may comprise a printed circuit board (PCB) and/or bemanufactured from any suitable printed circuit board materials or othermaterials capable of supporting propagation of RF signals in a desiredrange of frequencies. For example, substrate 700 may be manufacturedfrom materials that support propagation of microwave and/or millimeterwave RF signals. As one illustrative example, substrate 700 may bemanufactured from materials that support propagation of microwavesignals having frequencies in the range of 0.5-20 GHz, 4-6 GHz, 8-12GHz, 50-70 GHz, 100-140 GHz, 50 GHz-240 GHz, and/or any suitablefrequency range within the union combination of such ranges.

In some embodiments, the substrate 700 may include one or more layersand/or coatings for reducing the harmonic coupling between the transmitand receive antennas on the substrate. For example, the substrate 700may include a frequency selective surface (FSS) and/or an absorbentcoating, examples of which are provided herein. In some embodiments, thesubstrate 700 may include multiple layers, including one or more layershaving connections mapping the BGA pins 710 to the semiconductor diebond pads 708.

In some embodiments, the substrate 700 may include any suitablecircuitry (e.g., impedance matching circuitry, filtering circuitry) andtransmission lines (e.g., transmission lines 712) for transmitting RFsignals between the semiconductor die to be coupled to the substrate viabond pads 708 and antennas 704 and 706. In some embodiments, thesubstrate 700 may contain one or more additional circuits, chips, and/orother components of any kind as part of interrogator device or a targetdevice, as substrate 700 is not limited to including only the componentsillustrated in FIG. 7A.

In some embodiments, each of antennas 704 and 706 may be fabricated onsubstrate 700. For example, substrate 700 may comprise one or moreconductive layers and each of antennas 704 and 706 may be fabricated onthe substrate 700 at least in part by patterning the conductivelayer(s). In some embodiments, antenna 704 may be configured to transmitRF signals circularly polarized in a first rotational direction (e.g.,clockwise) and the antenna 706 may be configured to receive RF signalscircularly polarized RF in a second rotational direction different fromthe first rotational direction (e.g., counter-clockwise). In otherembodiments, however, each of antennas 704 and 706 may be configured totransmit and receive RF signals circularly polarized in the samerotational direction.

Each of antennas 704 and 706 may be a patch antenna, a planar spiralantenna, an antenna comprising a first linearly polarized antenna and asecond linearly polarized antenna disposed orthogonally to the firstlinearly polarized antenna, a folded dipole antenna, a MEMS antenna, orany other suitable type of antenna. In some embodiments, antennas 704and 706 may be configured to transmit/receive at any suitable (e.g.,millimeter wave and/or microwave) radio frequencies f₀/kf₀, where thetransmit antenna 704 may be configured to transmit RF signals having acenter frequency of f₀ and the receive antenna 706 may be configured toreceive RF signals having a center frequency of kf₀, which is a harmonicof f₀.

FIG. 7B is a diagram of an illustrative semiconductor die 722 beingprepared for bonding to the substrate of FIG. 7A, in accordance withsome embodiments of the technology described herein. The semiconductordie 722 may be a silicon die, for instance from a bulk silicon wafer orsilicon-on-insulator (SOI) wafer. In some embodiments, the die 722 maybe a single crystal silicon die. In some embodiments, the die 722 may bea CMOS die, a BiCMOS die, a GaAs die, a GaN die, or may be formed of anyother suitable semiconductor material. The semiconductor die 722 mayhave any of numerous types of circuitry integrated therewith, numerousexamples of such circuitry are provided herein.

In some embodiments, the semiconductor die may be flip-chip bonded tosubstrate 700. To this end, as shown in FIG. 7B, the chip die 722 mayinclude multiple bond pads 724 (e.g., the bond pads 724 may correspondto the plurality of bond pads 708 on substrate 700). As with bond padsor lands 708, while only four bond pads 724 are illustrated for clarity,any number of bonds pads may be present to provide the necessary firstlevel connections from the semiconductor die to substrate 700. Inaddition, it should be appreciated that the bond pads are not drawn toscale, but are depicted schematically for illustration. Each of bondpads 724 may be “bumped” with metal (e.g., copper) bumps 726. The bumps726 may be topped with solder tined tops 728 resulting in overallstructure 720. When the structure 720 is flipped onto the substrate 700,it may be bonded to the substrate by a suitable surface mount technologysuch as a solder reflow process resulting in the (unencapsulated) device730 shown in FIG. 7C.

In general, wire bonding the semiconductor die to the substrate providesa more economical solution. However, while wire bonding may be used insome embodiments, wire bonds are generally unsuitable formicro-localization systems operating in the GHz range. The inventorshave developed interrogator and target devices requiring relativelysmall numbers of bond pads, facilitating relatively inexpensive andsimple flip-chip bonding fabrication processes to be utilized.

The unencapsulated device 730 shown in FIG. 7C may be encapsulated toprotect the semiconductor die 722, for example, from moisture,oxidation, and/or any other environmental contaminants. For example, asshown in FIG. 7D, the device 730 may be encapsulated by applying acoating 742 around the outside edges of the die 722 to obtainencapsulated device 740. As another example, shown in FIG. 7E, thesemiconductor die 722 may be encapsulated with a blob of encapsulation752 to obtain encapsulated device 750. As another example, shown in FIG.7F, the die 722 and the substrate 700 may be both encapsulated withencapsulation 762 to obtain encapsulated device 760. The encapsulationmay be made of a material capable of supporting propagation of microwaveand/or millimeter wave RF signals (e.g., because the encapsulationcovers antennas 704 and 706). In some embodiments, the encapsulation 762may be considered as a part of antenna 704 and/or antenna 706, actinglike as a dielectric lens in some instances or an impedance match tofreespace in other instances.

Other packaging and interconnect techniques may be utilized as well,including ceramic or plastic covers, laminate (PCB) technologies, or anyother suitable packaging or interconnect solutions that suitably protectthe device from the environment and/or physical damage and that allowfor suitable first level connections between the semiconductor die andthe antenna and package (e.g., substrate 700) and allow for suitablesecond level connections between the packaged device and the next levelof interconnection (e.g., the system level board of a product into whichthe micro-localization components are integrated such as, for example,product 200).

FIG. 8A is a block diagram illustrating components of an interrogatordevice 800, in accordance with some embodiments of the technologydescribed herein. In the illustrative embodiment of FIG. 8A,interrogator device 800 includes waveform generator 110, transmit andreceive circuitry 112 a, transmit antenna 114, receive antenna 116, andcontrol circuitry 118. Transmit and receive circuitry 112 a includesfrequency multipliers 802, 804, 806, and 809, amplifiers 803, 805, 807,808, 810, 811, 813, and 814, frequency mixer 812, filter 815, andanalog-to-digital converter (ADC) 816. Each of the above-identifiedcomponents of transmit and receive circuitry 112 a may be of anysuitable type, as aspects of the technology described herein are notlimited in this respect.

As shown in FIG. 8A, RF signals generated by waveform generator 110 areprocessed in a series of three stages prior to being transmitted bytransmit antenna 114. In each stage, input RF signals are provided to afrequency multiplier circuit to obtain output signals having frequenciesat a harmonic of the frequencies of the input signals (e.g., eachfrequency multiplier may be a frequency doubler) and the output signalsare amplified at least in part to compensate for any loss induced by thenonlinear processing in the frequency multiplier circuit. For example,as shown in FIG. 8A, in the first stage of processing, RF signalsgenerated by waveform generator 110 are provided to frequency multiplier802 and the RF signals output by frequency multiplier 802 are amplifiedby amplifier 803. In the second stage of processing, RF signals outputby amplifier 803 are provided to frequency multiplier 804 and the RFsignals output by the frequency multiplier 804 are amplified byamplifier 805. In the third stage of processing, RF signals output byamplifier 805 are provided to frequency multiplier 806 and the RFsignals output by the frequency multiplier 806 are amplified byamplifier 807. The RF signals amplified by amplifier 807 are provided toamplifier transmit antenna 114.

In some embodiments, each of the frequency multipliers 802, 804, and 806may be a frequency doubler generating output signals whose frequency istwice that of the input signals. In such embodiments, RF signalsgenerated by the waveform generator as having a center frequency of f₀(e.g., 7.5 GHz) are transformed, through operation of frequencymultipliers 802, 804, and 806, to have a center frequency of 8f₀ (e.g.,60 GHz). Although in the illustrated embodiment three frequency doublersare used to increase the frequencies in the RF signals generated bywaveform generator 110 by a factor of 8, it should be appreciated thatinterrogator devices described herein are limited neither by the numberof frequency multipliers in the signal path between waveform generator110 and transmit antenna 114 nor by the multiplication factor induced byeach of the frequency multipliers in the signal path. For example, toachieve an “8×” multiplication factor, interrogator 800 may beimplemented with two frequency multipliers (instead of three frequencymultipliers as shown in FIG. 8A) one of which increases the frequenciesof input RF signals by a factor of four, and the other by a factor oftwo. As another example, interrogator 800 may be implemented with asingle frequency multiplier circuit configured to increase thefrequencies of input RF signals by a factor of eight.

It should also be appreciated that interrogator devices described hereinare not limited by the multiplication factor induced to the RF signalsgenerated by the waveform generator 110 by the circuitry in the transmitsignal chain between waveform generator 110 and transmit antenna 114.For example, in embodiments where the waveform generator 110 isconfigured to generate RF signals having a center frequency of f₀ andthe transmit antenna is configured to transmit RF signals having acenter frequency of kf₀ (where k is an integer such as, for example, 2,4, 8, 16, or 32), the circuitry in the transmit signal chain betweenwaveform generator 110 and transmit antenna 114 may be configured toincrease the frequency of the RF signals generated by waveform generatorby a factor of k. As one example, the circuitry in the transmit signalchain between waveform generator 110 and transmit antenna 114 may beconfigured to increase the frequency of the RF signals generated bywaveform generator by a factor of 8 when waveform generator 110generates having RF signals having a center frequency of 7.5 GHz andtransmit antenna 114 transmits at 60 GHz as shown in FIGS. 8A and 8B. Asyet another example, the circuitry in the transmit signal chain betweenwaveform generator 110 and transmit antenna 114 may be configured toincrease the frequency of the RF signals generated by waveform generatorby a factor of 4 when waveform generator 110 generates having RF signalshaving a center frequency of 15 GHz and transmit antenna 114 transmitsat 60 GHz. As yet another example, the circuitry in the transmit signalchain between waveform generator 110 and transmit antenna 114 may beconfigured to increase the frequency of the RF signals generated bywaveform generator by a factor of 2 when waveform generator 110generates having RF signals having a center frequency of 30 GHz andtransmit antenna 114 transmits at 60 GHz.

In some embodiments, transmit antenna 114 may be configured to transmitRF signals having a first center frequency and the receive antenna 116may be configured to receive RF signals having a second center frequencydifferent from the first center frequency. For example, the secondcenter frequency may be a harmonic of the first frequency such that thetransmit antenna 114 is configured to transmit RF signals having acenter frequency of f₀ and the receive antenna 116 is configured toreceive RF signals having a center frequency of 2f₀ (or any othersuitable harmonic of f₀. As one example, the transmit antenna 114 may beconfigured to transmit RF signals having a center frequency in the rangeof 4-6 GHz (e.g., 5 GHz) or in the range of 50-70 GHz (e.g., 60 GHz) andthe receive antenna 116 may be configured to receive RF signal having acenter frequency in the range of 8-12 GHz (e.g., 10 GHz) or in the rangeof 100-140 GHz (e.g., 120 GHz).

In some embodiments, transmit antenna 114 may be configured to transmitRF signals having one type of polarization and the receive antenna 116may be configured to receive RF signals having a different type ofpolarization. As discussed herein, such a configuration may beadvantageous in that it serves to reduce the effects of multipath on thesignals received by the interrogator device 800 in communication with atarget device (e.g., any target device described herein including withreference to FIGS. 9A-9H). For example, the transmit antenna 114 may beconfigured to transmit RF signals circularly polarized in a firstrotational direction and the receive antenna 116 may be configured toreceive RF signals circularly polarized in a second rotational directlydifferent (e.g., opposite) from the first rotational direction. As oneexample, the transmit antenna 114 may be configured to transmit RFsignals circularly polarized in a clockwise (or counter-clockwise)direction and the receive antenna 116 may be configured to receive RFsignals circularly polarized in the counter-clockwise (or clockwise)direction. Each of transmit antenna 114 and receive antenna 116 may beany suitable type of antenna, examples of which are provided herein. Insome embodiments, one or both of transmit antenna 114 and receiveantenna 116 may be differentially coupled to transmit and receivecircuitry 112 a.

As shown in FIG. 8A, RF signals received by receive antenna 116 areamplified by amplifier 811 and mixed, by frequency mixer 812, with atransformed version of RF signals transmitted by transmit antenna 114.In the illustrative embodiment of FIG. 8A, the RF signals output byfrequency multiplier 806 are both: (1) amplified by amplifier 807 and,subsequently, provided to transmit antenna 114 for transmission; and (2)transformed by signal transformation chain that includes amplifier 808,frequency multiplier 809, and amplifier 810 and, subsequently, providedto frequency mixer 812 for mixing with RF signals received by receiveantenna 116 and amplified by amplifier 811. The mixed RF signals outputby frequency mixer 812 are amplified by amplifiers 813 and 814, filteredby filter 815, and digitized by ADC 816 prior to be provided to controlcircuitry 118.

As discussed herein, in some embodiments, the interrogator device 800may transmit, to a target device, RF signals having a first centerfrequency f₀ and receive, from the target device, RF signals having asecond center frequency, which may be a harmonic of the first centerfrequency (e.g., 2f₀). In such embodiments, the target device may beconfigured to transform RF signals it receives from the interrogatordevice 800 (i.e., RF signals having the first center frequency) toobtain RF signals having the second center frequency. For this purpose,the target device may comprise signal transformation circuitry (e.g.,signal transformation circuitry 124 a described below with reference toFIG. 9A) for generating RF signals having the second center frequencyfrom received RF signals having the first center frequency.

As also described herein, interrogator device 800 is configured to usethe RF signals that it transmits to a target device and the RF signalsit receives from the target device in furtherance of determining thedistance between the interrogator device and the target device.Accordingly, in some embodiments, the interrogator device 800 maytransform the RF signals it transmits to the target device similarly tohow the target device may transform the RF signals it receives from theinterrogator device before transmitting them back to the interrogatordevice. In this way, the transmitted RF signals may be transformed bythe interrogator device to have the same center frequency as that of thereceived signals, which allows for the transformed RF signals and thereceived RF signals to be mixed using a frequency mixer to obtain amixed RF signal indicative of the distance between the interrogatordevice and the target device.

For example, as shown in FIG. 8A, the RF signals transmitted, to atarget device (e.g., target device 900 described with reference to FIG.9A), by interrogator device 800 may be transformed by frequencymultiplier 809 similarly to how a frequency multiplier in the targetdevice (e.g., frequency multiplier 908) transforms the RF signals itreceives from interrogator device 800. As one example, frequencymultiplier 809 and frequency multiplier 908 may each be frequencydoublers so that the interrogator device 800: (1) transmits, to targetdevice 900, RF signals having a center frequency f₀; (2) transforms theRF signals having a center frequency of f₀ to transformed RF signalshaving a center frequency of 2f₀; and (3) mixes the transformed RFsignals having a center frequency of 2f₀ with RF signals received fromthe target device 900, which received RF signals also have a centerfrequency of 2f₀, due to the processing performed on the target device(e.g., by frequency multiplier 908).

In the illustrative embodiment of FIG. 8A, transmitted RF signals aretransformed using frequency multiplier 809 to obtained transformed RFsignals having the same center frequency (e.g., 2f₀) as the RF signalsobtained by receive antenna 116. Thus, the RF signals being mixed byfrequency mixer 812, and subsequently digitized by ADC 816, have thecenter frequency of 2f₀. In other embodiments, instead of transformingtransmitted RF signals, the received RF signals may be transformedinstead by a frequency divider circuit to obtain transformed RF signalshaving the same center frequency (e.g., f₀) as the transmitted RFsignals. In such embodiments, the RF signals being mixed by frequencymixer 812, and subsequently digitized by ADC 816, have the centerfrequency of f₀, which may reduce the cost and/or improve theperformance of the frequency mixer 812 and/or ADC 816.

The interrogator device 800 may be manufactured in any of the waysdescribed herein. For example, in some embodiments, the interrogatordevice 800 may comprise a substrate (e.g., a printed circuit board)having the transmit antenna 114 and the receive antenna 116 fabricatedthereon, and a semiconductor die mounted to the substrate, coupled tothe transmit and receive antennas, and having transmit and receivecircuitry 112 a fabricated thereon. In such embodiments, the transmitand receive circuitry 112 a may be integrated circuitry monolithicallyintegrated with the semiconductor die. In some embodiments, thesemiconductor die may be flip-chip bonded to the substrate. In someembodiments, the substrate may comprise a printed circuit board havingat least one conductive layer, and the transmit antenna 114 and thereceive antenna 116 may be fabricated on the substrate by patterning theat least one conductive layer. Although, in some embodiments, one ormore portions of the interrogator device (e.g., transmit and receivecircuitry 112 a) may be part of integrated circuitry fabricated on asemiconductor die, in other embodiments, the same portion(s) may berealized as discrete components on the substrate (e.g., as discretecomponents mounted on a PCB substrate).

It should be appreciated that the embodiment illustrated in FIG. 8A isillustrative and that there are variations. For example, in someembodiments, there may be zero, one, two, three, or any other suitablenumber of amplifiers of any suitable type between any pair of circuitsshown in FIG. 8A. As another example, there may be zero, one, two,three, or any other suitable number of filters of any suitable typebetween any pair of circuits shown in FIG. 8A. As another example,although in the illustrated embodiment ADC 816 is part of transmit andreceive circuitry 112 a so that digitized waveforms are output from thetransmit and receive circuitry 112 a to control circuitry 118, in otherembodiments ADC 816 may not be part of transmit and receive circuitry112 a and, instead, may be further downstream in the processing chain.In such embodiments, analog waveforms may be output from the transmitand receive circuitry 112 a to control circuitry 118.

As described herein, waveform generator 110 may be configured togenerate any RF signals of any suitable type includingfrequency-modulated waveforms, in some embodiments. For example,waveform generator 110 may be configured to generate linear frequencymodulated waveforms (sometimes termed “chirps” herein). In someembodiments, including the embodiments illustrated in FIGS. 8B, 8C, and8D, waveform generator 100 may be configured to generate chirps using aclosed-loop approach relying on a phase-locked loop (PLL) to generatechirps at a desired frequency.

FIG. 8B is a block diagram of an illustrative interrogator device 825having waveform generator 110 b, transmit and receive circuitry 112 b,transmit antenna 114, and receive antenna 116. Waveform generator 110 bincludes a voltage-controlled oscillator 828 and chirp PLL circuitry 826configured to drive the voltage-controlled oscillator, via voltagesignals on line 827, to generate linear frequency modulated (LFM) RFsignals having a center frequency of 7.5 GHz. The generated chirps areprovided to chirp PLL circuitry 826 via feedback line 829, and also totransmit and receive circuitry 112 b via line 830. The chirp PLLcircuitry 826, line 827, VCO 828, and feedback line 829 constitute achirp phase locked loop.

It should be appreciated that chirp PLL circuitry 826 may be configuredto generate chirp waveforms in any of numerous ways including, but notlimited to, using a direct digital synthesizer in a so-called “sweptreference” approach that is discussed in more detail with reference toFIG. 13A, using an auxiliary input such as a step or an impulse toperturb the phase locked loop in a so-called “feedback loopperturbation” approach that is described in more detail with referenceto FIG. 13B, and using digital logic to step the frequency of a PLL in aso-called “stepped frequency” approach that is described in more detailwith reference to FIG. 13C.

In the embodiment of FIG. 8B, transmit and receive circuitry 112 bincludes frequency multiplier circuitry 832, frequency multipliercircuitry 836, amplifiers 834, 835, 838, and 842, and frequency mixer840. RF signals generated by waveform generator 110 b are provided tofrequency multiplier circuitry 832 via line 830. The frequencymultiplier circuitry 832 may be configured to multiply the frequenciesin the input RF signals by any suitable factor (e.g., by a factor of 2,4, 8, 16, etc.). In the illustrative embodiment of FIG. 8B, thefrequency multiplier circuitry 832 is configured to multiply thefrequencies in the input RF signals by a factor of eight so that, forexample, input RF signals having a center frequency of 7.5 GHz aretransformed by frequency multiplier circuitry 832 to RF signals having acenter frequency of 60 GHz. Frequency multiplier circuitry 832 may beimplemented in any suitable way and, for example, may be implementedusing a series of any suitable number of frequency multipliers andamplifiers. For instance, frequency multiplier circuitry may beimplemented using a series of frequency multipliers and amplifiers802-806 described with reference to FIG. 8A.

As shown in FIG. 8B, RF signals output by frequency multiplier circuitry832 are amplified using amplifiers 834 and 835 and, subsequently,provided to transmit antenna 114, which is configured to transmitmicrowave RF signals having a center frequency of 60 GHz. RF signalsoutput by frequency multiplier circuitry are also provided to frequencymultiplier circuitry 836, which further increases the frequencies in theRF signals by a factor of two (e.g., to match a similar transformationthat may be performed by a target device on RF signals transmitted bytransmit antenna 114 and received at the target device) to obtain RFsignals having a center frequency of 120 GHz. The RF signals output byfrequency multiplier circuitry 836 are amplified by amplifier 838 andmixed, using frequency mixer 840, with RF signals received from a targetdevice by receive antenna 116 and amplified by amplifier 842 to obtainmixed RF signals output from frequency mixer 840 on line 841. The mixedRF signals output on line 841 may be indicative of the distance betweeninterrogator device 825 and the target device. The mixed signals outputon line 841 may be further processed in any suitable way and, forexample, may be processed by one or more amplifiers and/or filters priorto being digitized using an ADC (e.g., as is the case for mixed RFsignals produced by frequency mixer 812 described with reference to FIG.8A).

Although in the illustrative embodiment of FIG. 8B the waveformgenerator 110 b is configured to generate chirped waveforms having acenter frequency of 7.5 GHz, this is not a limitation of aspects of thetechnology described herein, as the waveform generator 110 may beconfigured to generate chirped waveforms having any suitable centerfrequency.

As described herein, in some embodiments, an interrogator device maycomprise a transmit antenna configured to transmit RF signals having afirst center frequency f₀ and receive RF signals having a secondfrequency that is a harmonic of the first center frequency such as, forexample, 2f₀. In such embodiments, the waveform generator part in theinterrogator device may be configured to generate RF signals havingeither the first center frequency or the second center frequency. Thisallows for alternative transmit and receive circuitry designs includingthe designs shown in FIGS. 8C and 8D.

FIG. 8C is a block diagram of an illustrative interrogator device 850having waveform generator 110 c, transmit and receive circuitry 112 c,transmit antenna 114, and receive antenna 116. Waveform generator 110 cincludes a voltage-controlled oscillator 828 and chirp PLL circuitry 826configured to drive the voltage-controlled oscillator, via voltagesignals on line 827, to generate linear frequency modulated (LFM) RFsignals having a center frequency of 60 GHz. The generated chirps areprovided to transmit and receive circuitry 112 c via line 851.

In the embodiment of FIG. 8C, transmit and receive circuitry 112 cincludes frequency multiplier circuitry 836, amplifiers 854, and 834,835, 838, and 842, frequency mixer 840, and frequency dividers 856, 857,and 858. Relative to the transmit and receive circuitry 112 b of FIG.8B, transmit and receive circuitry 112 c does not include frequencymultiplier 832 because the waveform generator 110 c generates microwaveRF signals having a center frequency of 60 GHz (unlike waveformgenerator 110 b that generates microwave RF signals having a centerfrequency of 7.5 GHz, which needs to be increased by a factor of eightprior to transmission by transmit antenna 14 that is configured totransmit RF signals having a center frequency of 60 GHz). RF signalshaving a center frequency of 60 GHz and amplified by amplifier 834 notonly are provided to amplifier 835 and, subsequently transmit antenna114, but also to a series of frequency dividers 856, 857, and 858 toprovide RF signals having a center frequency of 7.5 GHz, which areprovided via line 852 to chirp PLL circuitry 826 thereby providing afeedback loop. Whereas line 829 provided the feedback loop for the chirpPLL in the embodiment of FIG. 8B, the feedback loop in the embodiment ofFIG. 8C includes line 851, amplifiers 854 and 834, frequency dividers856-858 and line 852.

FIG. 8D is a block diagram of an illustrative interrogator device 860having waveform generator 110 d, transmit and receive circuitry 112 d,transmit antenna 114, and receive antenna 116. Waveform generator 110 dincludes a voltage-controlled oscillator 828 and chirp PLL circuitry 826configured to drive the voltage-controlled oscillator, via voltagesignals on line 827, to generate linear frequency modulated (LFM) RFsignals having a center frequency of 120 GHz. The generated chirps areprovided to transmit and receive circuitry 112 c via line 861.

In the embodiment of FIG. 8D, transmit and receive circuitry 112 dincludes amplifiers 834, 835, 838, 842, and 866, frequency mixer 840,and frequency dividers 864, and 856, 857, and 858. Relative to thetransmit and receive circuitry 112 c of FIG. 8C, transmit and receivecircuitry 112 d does not include frequency multiplier 836 because thewaveform generator 110 d generates microwave RF signals having a centerfrequency of 120 GHz (unlike waveform generator 110 c that generatesmicrowave RF signals having a center frequency of 60 GHz, which needs tobe increased by a factor of two prior to being mixed with RF signalsreceived by receive antenna 16 that is configured to transmit RF signalshaving a center frequency of 120 GHz). RF signals having a centerfrequency of 120 GHz and amplified by amplifier 834 are provided tofrequency divider 864 to obtain RF signals having a center frequency of60 GHz, which signals are: (1) transmitted by transmit antenna 14 afteramplification by amplifiers 866 and 834; and (2) fed back to waveformgenerator 110 d via the series of frequency dividers 856, 857, and 858to provide RF signals having a center frequency of 7.5 GHz, which areprovided via line 862 to chirp PLL circuitry 826 thereby providing afeedback loop. Accordingly, in the embodiment of FIG. 8D, the feedbackloop includes line 861, amplifiers 854 and 834, frequency dividers856-858 and 864, and line 862.

As discussed above, in some embodiments, an interrogator device maycomprise a waveform generator configured to generate linear frequencymodulated (LFM) RF signals (RF chirps). In some embodiments, a waveformgenerator may be configured to generate RF chirps using a phase lockedloop (PLL). Illustrative examples of such a closed loop approach aredescribed below with reference to FIGS. 13A, 13B, and 13C. It should beappreciated, however, that a waveform generator is not limited to usinga PLL to generate RF chirps and, for example, may be configured to usean open-loop (non PLL controlled) oscillator to synthesize RF chirps. Itshould also be appreciated that a waveform generator is not limited togenerating RF chirps and may be configured to generate any othersuitable RF signals, including any of the RF signals described herein,as aspects of the technology described herein are not limited in thisrespect.

FIG. 13A is a block diagram illustrating waveform generator circuitry1300 configured to generate linear frequency modulated waveforms using aphase locked loop, in accordance with some embodiments of the technologydescribed herein. Waveform generator circuitry 1300 may be part of anywaveform generator described herein including, by way of example and notlimitation, waveform generators 110, 110 b, 110 c, and 110 d describedabove with reference to FIGS. 8A-D.

The waveform generator circuitry 1300 is configured to generate RFchirps using a direct digital synthesizer 1310 in a so-called “sweptreference” approach. As shown in FIG. 13A, waveform generator circuitry1300 includes a voltage controlled oscillator (VCO) 1302, signalsplitter 1304, programmable digital divider 1306 that is programmable byinput provided via line 1305, frequency multiplier 1308, direct digitalsynthesizer 1310, and loop filter 1312. The DDS 1310 operates as areference oscillator for the resulting phase locked loop.

In some embodiments, the DDS 1310 may be a digital synthesizer thatstores (e.g., in a memory part of DDS 1310) values for a digitalwaveform (e.g., a sinusoid, a chirp, or any other suitable waveform).The DDS 1310 may be configured to “play back” the stored values througha digital to analog converter (DAC). That is, the DDS 1310 may beconfigured to process the stored values using a DAC, which may be partof the DDS 1310 in some embodiments, and output the resulting analogvalues. The rate at which the DDS 1310 outputs the stored values for thedigital waveform may determine its output frequency. In someembodiments, the DDS 1310 may be chirp-modulated above and below acenter reference clock frequency, thereby causing the output of the VCO1302 to chirp at its carrier frequency. The DDS 1310 may be chirpmodulated in any of a variety of ways. For example, in some embodiments,the DDS 1310 may store a fixed-frequency sinusoid and modulate the rateat which it is played back. Modulating the rate of playback linearlyover the length of the sinusoid results in a chirp being generated bythe DDS 1310. In other embodiments, the DDS 1310 may simply store achirp and play it back at a fixed playback rate. The output of DDS 1310is multiplied-up in the PLL thereby providing a chirp at the microwavefrequency of interest at the RF Out line 1307.

In some embodiments, waveform generator circuitry 1300 may be generatedat least in part on a semiconductor die. For example, as shown in FIG.13A, oscillator 1302, signal splitter 1304, programmable digital divider1306, and frequency mixer 1308 may be realized as integrated circuitryfabricated on a semiconductor die part of the interrogator. On the otherhand, direct digital synthesizer 1310 and loop filter 1312 may beimplemented off the semiconductor die, for example, as discretecomponents on a substrate. However, in other embodiments, all, none or adifferent subset of the components of waveform circuitry 1300 may berealized as integrated circuitry fabricated on a semiconductor die partof the interrogator.

FIG. 13B is a block diagram illustrating waveform generator circuitry1320 configured to generate frequency-modulated waveforms using a phaselocked loop, in accordance with some embodiments of the technologydescribed herein. Waveform generator circuitry 1320 may be part of anywaveform generator described herein including, by way of example and notlimitation, waveform generators 110, 110 b, 110 c, and 110 d describedabove with reference to FIGS. 8A-D.

The waveform generator circuitry 1320 is configured to generate RFchirps using an auxiliary input such as a step or an impulse to perturbthe phase locked loop in a so-called “feedback loop perturbation”approach. As shown in FIG. 13B, waveform generator circuitry 1320includes a voltage controlled oscillator (VCO) 1322, signal splitter1324, programmable digital divider 1326 that is programmable by inputprovided via line 1325, frequency multiplier (sometimes termed “phasecomparator”) 1328, summation block 1330, and loop filter 1332.Additionally, waveform generator circuitry includes a fixed frequencyreference oscillator 1336 (e.g., a quartz crystal) and a step/impulsegenerator 1334. The summation block 1330 is within the PLL so that astep and/or impulse generated by step/impulse generator 1334 may be feddirectly into the loop thereby perturbing the loop to sweep up to adesired frequency then correct-back-down to its programmed frequency.This perturbation in the feedback loop would cause an up-then-downchirp, relying on a second order transfer function of the loop filter1332 so that the output provided on line 1327 is a linear chirp. Thisfeedback loop perturbation technique may be less precise than the PLLtechniques described with reference to FIGS. 13A and 13C, but may becheaper to implement.

In some embodiments, waveform generator circuitry 1320 may be fabricatedat least in part on a semiconductor die. For example, as shown in FIG.13B, oscillator 1322, signal splitter 1324, programmable digital divider1326, and frequency mixer 1328, and summation block 1330 may be realizedas integrated circuitry fabricated on a semiconductor die part of theinterrogator. On the other hand, loop filter 1332, step/impulsegenerator 1334, and fixed-frequency reference oscillator 1336 may beimplemented off the semiconductor die, for example, as discretecomponents on a substrate. However, in other embodiments, all, none or adifferent subset of the components of waveform circuitry 1320 may berealized as integrated circuitry fabricated on a semiconductor die partof the interrogator.

FIG. 13C is a block diagram illustrating waveform generator circuitry1340 configured to generate frequency-modulated waveforms using a phaselocked loop, in accordance with some embodiments of the technologydescribed herein. Waveform generator circuitry 1340 may be part of anywaveform generator described herein including, by way of example and notlimitation, waveform generators 110, 110 b, 110 c, and 110 d describedabove with reference to FIGS. 8A-D.

The waveform generator circuitry 1340 is configured to generate RFchirps using digital logic to step the frequency of a PLL in a so-called“stepped frequency” approach. As shown in FIG. 13C, waveform generatorcircuitry 1340 includes a voltage controlled oscillator (VCO) 1341,signal splitter 1342, programmable digital divider 1344 that is coupledto digital control logic block 1346, frequency multiplier 1348,fixed-frequency reference oscillator 1352 (e.g., a quartz crystal), andloop filter 1350. The frequency of the PLL in waveform generatorcircuitry 1340 may be digitally stepped by commands sent to programmabledigital divider 1344 from the digital control logic block 1346 (oranother device such as a microprocessor or FPGA). These frequency stepcommands may be linear steps in frequency. The second-order response ofloop filter 1350 may smooth over the frequency steps so that the outputprovided on line 1347 is a smooth linear FM chirp.

In some embodiments, waveform generator circuitry 1340 may be fabricatedat least in part on a semiconductor die. For example, as shown in FIG.13C, oscillator 1341, signal splitter 1342, programmable digital divider1344, digital control logic block 1346, and frequency mixer 1348 may berealized as integrated circuitry fabricated on a semiconductor die partof the interrogator. On the other hand, loop filter 1350 andfixed-frequency reference oscillator 1352 may be implemented off thesemiconductor die, for example, as discrete components on a substrate.However, in other embodiments, all, none or a different subset of thecomponents of waveform circuitry 1340 may be realized as integratedcircuitry fabricated on a semiconductor die part of the interrogator.For example, in some embodiments, digital control logic block 1346 maybe implemented off chip.

FIG. 9A is a block diagram illustrating components of a target device900, in accordance with some embodiments of the technology describedherein. In the illustrative embodiment of FIG. 9A, target device 900includes receive antenna 122, signal transformation circuitry 124 a, andtransmit antenna 126. The output of receive antenna 122 is coupled, vialine 902, to an input of signal transformation circuitry 124 a. Theoutput of signal transformation circuitry 124 a is coupled, via line914, to transmit antenna 126.

As shown in FIG. 9A, signal transformation circuitry 124 a includesamplifier 904, frequency multiplier 908, and amplifier 912. Signalsoutput by receive antenna 122 may be provided to amplifier 904 via line902. The amplifier 904 amplifies signals received via line 902 andprovides the amplified signals to frequency multiplier 908 via line 906.The frequency multiplier 908 generates output signals whose frequency isa multiple of the frequency of the input signals received via line 906and provides the output signals to amplifier 912 via line 910. Theamplifier 912 amplifies signals received via line 910 and provides theamplified signals to the transmit antenna 126 via line 914.

In some embodiments, frequency multiplier 908 may receive input signalshaving a center frequency of f₀ and generate output signals having acenter frequency that is an integer multiple of f₀. For example,frequency multiplier 908 may receive input signals having a centerfrequency of f₀ and generate output signals having a center frequency of2f₀, 3f₀, 4f₀, 8f₀, 10f₀, or any other suitable integer multiple of f₀,as aspects of the technology described herein are not limited in thisrespect. As one example, in some embodiments, frequency multiplier 908may receive input signals having a center frequency in a range of 50-70GHz (e.g., 61.25 GHz) and generate output signals having a centerfrequency in a range of 100-140 GHz (e.g., 122.5 GHz). As anotherexample, in some embodiments, frequency multiplier 908 may receive inputsignals having a center frequency in a range of 4-6 GHz (e.g., 5 GHz)and generate output signals having a center frequency of 8-12 GHz (e.g.,10 GHz).

In some embodiments, frequency multiplier 908 may be implemented as acascade of frequency multipliers, which cascade may include one or moreamplifiers, isolators, and/or one or more filters between successivefrequency multipliers. For example, in some embodiments, frequencymultiplier 908 may be configured to output signals having a centerfrequency that is four times the center frequency of the input signalsprovided to frequency multiplier 908. In such an example, frequencymultiplier may be implemented as a single “4×” frequency multiplier or asequence of two “2×” frequency multipliers, each of which is configuredto output signals having a center frequency that is double the centerfrequency of the input signals provided to it. One or more amplifiersand/or filters may be provided between the “2×” frequency multipliers.

In some embodiments, frequency multiplier 908 may include a non-linearcircuit. The non-linear circuit may distort input signals provided tofrequency multiplier 908 to generate signals having center frequenciesthat are multiples of the center frequencies of the input signals.Additionally, frequency multiplier 908 may include one or more (e.g.,bandpass) filters for selecting a desired center frequency for theoutput signals (e.g., a desired harmonic frequency) and removing thefundamental and/or one or more other harmonic frequency components fromthe non-linearly distorted signals.

In some embodiments, the non-linear circuit in a frequency multiplier908 may be a diode. Frequency multiplier 908 may be any suitable type ofdiode frequency multiplier. For example, in some embodiments, frequencymultiplier 908 may be a Schottky diode, a silicon diode, a varistor-typediode frequency multiplier, a varactor-type frequency multiplier, a steprecover diode frequency multiplier, or a PIN diode frequency multiplier,any (e.g., all) of which may or may not be biased with a quiescent biascurrent.

In the illustrated embodiment of FIG. 9A, each of amplifiers 904 and 912may be of any suitable type and may be used to induce any suitableamount of gain to the input signals. In some embodiments, the gain ofamplifier 904 may be greater than the gain of amplifier 912, and, insome instances, may be significantly greater than the gain of amplifier912. For example, the gain of amplifier 904 may be at least 10, 20, 30,40, 50, or 100 times the gain of amplifier 912. Having amplifier 904induce a greater amount of gain than amplifier 912 provides as muchdrive power as possible to the frequency multiplier. In addition, lesspower is needed to induce power gain at lower frequencies (before thesignals pass through a frequency multiplier) than to induce the sameamount of power gain at higher frequencies (after the signals passthrough the frequency multiplier). Thus, inducing a greater amount ofgain via amplifier 904, reduces the overall power consumptionrequirements of the signal transformation circuitry, which isadvantageous.

As may be appreciated from FIG. 9A, the inclusion of frequencymultiplier 908 in the signal transformation circuitry 124 a causes RFsignals output to transmit antenna 126, via line 914, to have higherfrequencies than the RF signals input from the receive antenna 122, vialine 902. Accordingly, in some embodiments, receive antenna 122 may beconfigured to receive RF signals having a first center frequency andtransmit antenna 126 may be configured to transmit RF signals having asecond center frequency different from the first center frequency. Forexample, the second center frequency may be a harmonic of the firstfrequency. As a specific example, the second center frequency may betwice the first center frequency (e.g., when the frequency multiplier908 receives input signals having a center frequency of f₀ and generatesoutput signals having a center frequency of 2f₀).

In some embodiments, the receive antenna 122 may be configured toreceive RF signals having one type of polarization and the transmitantenna 126 may be configured to transmit RF signals having a differenttype of polarization. As discussed herein, such a configuration may beadvantageous in that it serves to reduce the effects of multipath on thesignals received by an interrogator device in communication with targetdevice 900. For example, the receive antenna 122 may be configured toreceive RF signals circularly polarized in a first rotational directionand the transmit antenna 126 may be configured to transmit RF signalscircularly polarized in a second rotational direction different (e.g.,opposite) from the first rotational direction. As a specific example,the receive antenna 122 may be configured to receive RF signalscircularly polarized in a clockwise (or counter-clockwise) direction andthe transmit antenna 126 may be configured to receive RF signalscircularly polarized in the counter-clockwise (or clockwise) direction.Each of receive antenna 122 and transmit antenna 126 may be any suitabletype of antenna, examples of which are provided herein.

The target device 900 may be manufactured in any of the ways describedherein. For example, in some embodiments, the target device 900 maycomprise a substrate (e.g., a printed circuit board) having the receiveantenna 122 and transmit antenna 126 fabricated thereon, and asemiconductor die mounted to the substrate, coupled to the receive andtransmit antennas, and having signal transformation circuitry 124 afabricated thereon. In such embodiments, signal transformation circuitry124 a may be integrated circuitry monolithically integrated with thesemiconductor die. In some embodiments, the semiconductor die may beflip-chip bonded to the substrate. In some embodiments, the substratemay comprise a printed circuit board having at least one conductivelayer, and the receive antenna 122 and the transmit antenna 126 may befabricated on the substrate by patterning the at least one conductivelayer. Although, in some embodiments, one or more portions of the targetdevice (e.g., signal transformation circuitry 124 a) may be part ofintegrated circuitry fabricated on a semiconductor die, in otherembodiments, the same portion(s) may be realized as discrete componentson the substrate (e.g., as discrete components mounted on a PCBsubstrate).

It should be appreciated that the embodiment illustrated in FIG. 9A isillustrative and that there are variations. For example, although in theillustrated embodiment a single amplifier 904 is shown between receiveantenna 122 and frequency multiplier 908, in other embodiments there maybe zero, two, three, four, five or more amplifiers between receiveantenna 122 and frequency multiplier 908. As another example, althoughin the illustrated embodiment, a single amplifier 912 is shown betweenfrequency multiplier 908 and transmit antenna 126, in other embodimentsthere may be zero, two, three, four, five or more amplifiers betweenfrequency multiplier 908 and transmit antenna 126. In some embodiments,the number and gain of the amplifiers in the signal chain from receiveantenna 122 to transmit antenna 126 may be determined based on anoverall amount of gain desired to induce to the signal and in view of anamount of loss induced by the frequency multiplier 908. For example, insome embodiments, a frequency multiplier (e.g., multiplier 908) mayinduce a 6 dB-12 dB loss to the power of the signals, and one ormultiple amplifiers (e.g., amplifiers 904 and 912) that provide at least30 dB of gain overall may be introduced into the signal chain betweenreceive antenna 122 and transmit antenna 126.

As another example of a variation of the embodiments shown in FIG. 9A,there may be one or more filters between any pair of circuits along thesignal path from receive antenna 122 to transmit antenna 126. As yetanother example, in the embodiment of FIG. 9A receive antenna 122 andtransmit antenna 126 are each coupled to signal transformation circuitry124 a using single lines 902 and 914, respectively. However, in otherembodiments, one or both of receive antenna 122 and transmit antenna 126may be differentially coupled to signal transformation circuitry 124 a.One such embodiment is shown in FIG. 9B, where both antennas aredifferentially coupled to the signal transformation circuitry.

In the illustrative embodiment of FIG. 9B, target device 915 includesreceive antenna 122, signal transformation circuitry 124 b, and transmitantenna 126. Receive antenna 122 is differentially coupled, via lines916 a and 916 b, to inputs of signal transformation circuitry 124 b.Transmit antenna 126 is differentially coupled to signal transformationcircuitry 124 b, whereby outputs of signal transformation circuitry 124b are provided, via lines 928 a and 928 b, to transmit antenna 126.Receive antenna 122 may be any suitable type of receive antenna,examples of which are provided herein. Transmit antenna 126 may be anysuitable type of transmit antenna, examples of which are providedherein.

As shown in FIG. 9B, signal transformation circuitry 124 b includesdifferential amplifier 918, frequency multiplier 922, and differentialamplifier 926. Signals output by receive antenna 122 may be provided todifferential amplifier 918 via lines 916 a and 916 b. The differentialamplifier 918 may amplify the difference between signals received vialine 916 a and 916 b, and may provide the resulting amplified signal tofrequency multiplier 922 via line 920. The frequency multiplier 922 maygenerate output signals whose frequency is a multiple of the frequencyof the input signals received via line 920, and may provide the outputsignals to differential amplifier 926 via line 924 a. The differentialamplifier 912 may receive input signals via line 924 a and ground 924 b,and may amplify the difference between the received signals and providethe amplified signals to the transmit antenna 126 via lines 928 a and928 b.

In the illustrated embodiment of FIG. 9B, frequency multiplier 922 maybe of any suitable type including any of the types described withreference to frequency multiplier 908 shown in FIG. 9A. Each ofamplifiers 918 and 926 may be of any suitable type and may be used toinduce any suitable amount of gain to the input signals.

In the embodiment of FIG. 9A, none of the components in the signal chainfrom receive antenna 122 to transmit antenna 126 are differentiallycoupled. On the other hand, in the embodiment of FIG. 9A, multiplecomponents in the signal chain are differentially coupled. It should beappreciated the embodiments of FIGS. 9A and 9B are illustrative examplesof ways in which components in the target device signal processingcircuitry may be coupled, and that any suitable pairs of consecutivecomponents in the signal processing chain from receive antenna 122 totransmit antenna 126 may be differentially coupled to one another. Forexample, in some embodiments, none, one, or more than one of thefollowing pairs of components may be differentially coupled: receiveantenna 122 and amplifier 918, amplifier 918 and frequency multiplier922, frequency multiplier 922 and amplifier 926, amplifier 926 andtransmit antenna 126. Additionally, to the extent the signal chainbetween receive antenna 122 and transmit antenna 126 includes one ormore other components (e.g., one or more amplifiers and/or filters),none, one, or multiple of these components may be differentially coupledto other components in the signal chain.

The target device 915 may be manufactured in any of the ways describedherein including in any of the ways described with reference to targetdevice 900. For example, in some embodiments, the target device 915 maycomprise a substrate having the receive antenna 122 and transmit antenna126 fabricated thereon, and a semiconductor die mounted to thesubstrate, coupled to the receive and transmit antennas, and havingsignal transformation circuitry 124 b fabricated thereon. In suchembodiments, signal transformation circuitry 124 b may be integratedcircuitry monolithically integrated with the semiconductor die.

FIG. 9C is a block diagram illustrating components of a target device930, in accordance with some embodiments of the technology describedherein. In the illustrative embodiment of FIG. 9C, target device 930includes receive antenna 122, signal transformation circuitry 124 c, andtransmit antenna 126. The output of receive antenna 122 is coupled, vialine 933, to an input of signal transformation circuitry 124 c. Theoutput of signal transformation circuitry 124 c is coupled, via line946, to transmit antenna 126. Receive antenna 122 may be any suitabletype of receive antenna, examples of which are provided herein. Transmitantenna 126 may be any suitable type of transmit antenna, examples ofwhich are provided herein.

Signal transformation circuitry 124 c may be configured to: (1)transform the frequency content of signals received from receive antenna122 by mixing the received signals with signals generated, using thetarget device, using one or more local oscillators; and (2) provide thetransformed signals to transmit antenna 126. For example, signalsreceived via receive antenna 122 and having a center frequency of f₀ maybe mixed with signals generated by a local oscillator part of the signaltransformation circuitry 124 c and having a center frequency of f₁ togenerate signals (heterodynes) having a center frequency of f₀+f₁.Signal transformation circuitry 124 c may be configured to generatesignals having any suitable center frequency f₁, and for example, may beconfigured to generate signals having center frequency f₀ (or othermultiple of f₀) such that once they are mixed with signals received byreceive antenna 122, the resulting signals will have a frequency of 2f₀(or any other multiple of f₀). For example, signal transformationcircuitry may be configured to generate signals having a centerfrequency in the range of 50-70 GHz (e.g., 61.25 GHz) that, when mixedwith signals received by receive antenna 122 having a center frequencyalso in the range of 50-70 GHz (e.g., 61.25 GHz), produce signals havinga center frequency in the range of 100-140 GHz (e.g., 122.5 GHz).

As shown in FIG. 9C, RF signals output by receive antenna 122 may beprovided, via line 933, to amplifier 940, which may amplify the signalsand provide the amplified signals to filter 942. Filter 942 may be ahigh-pass or any other suitable type of filter and may filter signalsreceived from amplifier 940 and provide the filtered signals toamplifiers 944 and 946. Signals amplified by amplifiers 944 and 946 maybe filtered by filter 948 and subsequently provided to one of the inputsof frequency mixer 945. The other input of frequency mixer 945 receivessignals generated by the signal chain that begins with signals generatedby local oscillator 932. The signals output by local oscillator 932 maybe provided to frequency multiplier 934 and subsequently to amplifier936. Signals amplified by amplifier 936 are provided to frequency mixer945.

In some embodiments, a single local oscillator 932 (of any suitabletype) may be used to generate signals for mixing with signals obtainedvia receive antenna 122. In other embodiments, multiple oscillators maybe used to generate such signals. For example, in some embodiments,including the embodiment illustrated in FIG. 9C, increased stability inthe signal generated by local oscillator 932 may be obtained by couplinglocal oscillator 932 to a controlled local oscillator 931. Controlledlocal oscillator 931 may be an oven-controlled oscillator, atemperature-controlled oscillator, and/or any other suitable type ofcontrolled oscillator. In such embodiments, local oscillator 932 maycomprise a phase-locked loop having output of the controlled oscillator931 as the reference signal such that the phases of signals produced bylocal oscillator 932 are synchronized with the phases of signalsproduced by controlled local oscillator 931. The frequency of signalsproduced by local oscillator 932 may be a multiple of the frequency ofsignals produced by controlled local oscillator 931.

In the illustrated embodiment of FIG. 9C, each of amplifiers 936, 940,944, 946 may be of any suitable type and may be used to induce anysuitable amount of gain to the input signals. Frequency multiplier 934may be of any suitable type including any of the types described withreference to frequency multiplier 908 with reference to FIG. 9A. Each offilters 942 and 948 may be of any suitable type (e.g., high-pass,low-pass, and band-pass). Frequency mixer 945 may be of any suitabletype and may be implemented using one or more non-linear elements suchas by using one or more diodes.

In some embodiments, target device 930 may have multiple modes includingan “awake” mode and a “sleep” mode. During the awake mode, the targetdevice 930 may be configured to receive signals via receive antenna 122,transform the received signals using signal transformation circuitry 124c, and transmit the transformed signals via transmit antenna 126. Duringthe sleep mode, one or more components of the target device 930 may beturned off such that the target device does not transmit signals viatransmit antenna 126.

In some embodiments, the target device 930 may be configured switchbetween the awake and sleep modes in response to a communicationreceived from an external device. In the illustrative embodiment of FIG.9C, for example, the auxiliary receiver 938 may be configured to receivea communication from an external device and, in response to thecommunication, turn off one or more of the amplifiers 936, 942, 944, and946, thereby putting target device 930 into sleep mode. It should beappreciated that although in the illustrative embodiment of FIG. 9C,auxiliary receiver 938 is shown as part of signal transformationcircuitry 124 c, in other embodiments, auxiliary receiver 938 may bepart of any other suitable circuitry of the target device. For example,in some embodiments, target device 930 may include control circuitry(e.g., control circuitry 128 described with reference to FIG. 2) and/oran external communications module (e.g., external communications module130 described with reference to FIG. 2) and auxiliary receiver 938 maybe part of the control circuitry or the external communications module.Auxiliary receiver 938 may be of any suitable type and, for example, maybe a ZigBee compatible module such that the auxiliary receiver 938 isconfigured to communicate according to one or more IEEE 802.15.4-basedcommunication protocols.

The target device 930 may be manufactured in any of the ways describedherein including in any of the ways described with reference to targetdevice 900. For example, in some embodiments, the target device 930 maycomprise a substrate having the receive antenna 122 and transmit antenna126 fabricated thereon, and a semiconductor die mounted to thesubstrate, coupled to the receive and transmit antennas, and having atleast some (e.g., all) of signal transformation circuitry 124 cfabricated thereon. In such embodiments, signal transformation circuitry124 c may be integrated circuitry monolithically integrated with thesemiconductor die. In some embodiments, all of signal transformationcircuitry 124 c may be fabricated on the semiconductor die. In otherembodiments, one or more components of signal processing circuitry 124 c(e.g., reference oscillator 931) may be on the substrate but off thedie. In yet other embodiments, no semiconductor die may be used. Forexample, in some embodiments, each of the components of signalprocessing circuitry 124 c may be realized as discrete componentscoupled to a substrate, such as a printed circuit board, for example.

It should be appreciated that the embodiment of FIG. 9C is illustrativeand that there are variations. For example, each instance of anamplifier in the signal transformation circuitry 124 c may be replacedby zero, two, or more than two amplifiers in other embodiments. As onespecific example, although there is a single amplifier 936 betweenfrequency multiplier 934 and frequency mixer 945 in the embodiment ofFIG. 9C, there may be zero or multiple amplifiers between the frequencymultiplier 934 and frequency mixer 945 in other embodiments. As anotherexample, the signal chain between receive antenna 122 and frequencymixer includes three amplifiers and two filters in the embodiment ofFIG. 9C, other embodiments may include any suitable number amplifiersand/or filters arranged in any suitable way, as aspects of thetechnology described herein are not limited in this respect. As anotherexample, although there is a single frequency multiplier 934 in thesignal chain from local oscillator 932 to frequency mixer 945, there maybe zero or multiple frequency mixers in this chain depending on thefrequency of signals generated by local oscillator 932 and the desiredfrequency of signals output by frequency mixer 945. As another example,any two consecutive components in target device 930 may bedifferentially coupled. For example, each of receive antenna 122 andtransmit antenna 126 may be differentially coupled to signaltransformation circuitry 126 c.

As may be appreciated from the foregoing, in some embodiments, RFsignals received by receive antenna 122 and having a first centerfrequency (e.g., f₁=5.5 GHz) may be mixed with RF signals generatedonboard target device 930 and having a second center frequency (e.g.,f₂=18.5 GHz) to obtain RF signals having a third center frequency thatis the sum of the first and second center frequencies (e.g., f₃=f₂+f₁=24GHz). In such embodiments, the output of the frequency mixer 945 is theheterodyne signal corresponding to the sum of the frequencies of theinput signals. In other embodiments, however, RF signals received byreceive antenna 122 and having a first center frequency (e.g., f₁=5.5GHz) may be mixed with RF signals generated onboard target device havinga second center frequency (e.g., 29.5 GHz) to obtain RF signals having athird center frequency that is the difference of the first and secondcenter frequencies (e.g., f₃=f₂−f₁=24 GHz). In such embodiments, theoutput of the frequency mixer 945 is the heterodyne signal correspondingto the difference of the frequencies of the input signals.

Another variation of the embodiment of FIG. 9C is one in which targetdevice 930 further comprises an automatic frequency control circuit(AFC) to compensate for any drift in the frequency generated by one ormore oscillators onboard the target device (e.g., oscillator 932). TheAFC circuit may be configured to sense the difference between the actualoscillator frequency and the frequency that is desired and produces,based on this sensed difference, a control voltage proportional to thedifference. In turn, the control voltage may be used to compensate forany drift in the frequency generated by one or more oscillators onboardthe target device, which drift may result from variations intemperature, loading, and/or for any other reason. Any suitable AFCcircuit may be used as part of target device 930, as aspects of thetechnology described herein are not limited in this respect.Additionally, in some embodiments, any suitable AFC circuit may be usedas part of an interrogator that interrogates target device 930.

Another variation of the embodiment of FIG. 9C is illustrated in FIG.9D, which shows a target device 935 that includes receive antenna 122, asecond receive antenna 123, signal transformation circuitry 124 d, andtransmit antenna 126. Antennas 122, 123, and 126 may be of any suitabletype of antenna, examples of which are provided herein. In thisembodiment, instead of relying on a reference signal produced locally atthe target device by oscillators 931 and 932 as shown in FIG. 9C, targetdevice 935 receives a continuous wave reference signal via receiveantenna 123. The continuous wave reference signal is then provided toamplifier 941 and filter 943 prior to being provided to frequencymultiplier 934. In this way, the target device need not include a localoscillator, which may be expensive to manufacture as part of the targetdevice, and receives a reference signal rather synthesizing it on itsown. In this way, the cost of manufacturing the target device may bereduced.

FIG. 9E is a block diagram illustrating components of a target device950, in accordance with some embodiments of the technology describedherein. In the illustrative embodiment of FIG. 9E, target device 950includes receive antenna 122, signal transformation circuitry 124 e, andtransmit antenna 126. The output of receive antenna 122 is coupled to aninput of signal transformation circuitry 124 e. The output of signaltransformation circuitry 124 e is coupled to an input of transmitantenna 126. Receive antenna 122 and transmit antenna 126 may be of anysuitable type, examples of which are provided herein.

As shown in FIG. 9E, signal transformation circuitry 124 e includesamplifier 952, filter 954 and frequency multiplier 956. Signals receivedby receive antenna 122 are provided to amplifier 952 via line 951.Signals amplified by amplifier 952 are provided, via lines 953, tofrequency multiplier 956 and to filter 954. Signals filtered by filter954 are fed back to amplifier 952 via line 955. The frequency multiplier956 generates output signals whose frequency is a multiple of thefrequency of the input signals received from amplifier 952, via lines953, and provides the output signals to transmit antenna 126 via line957.

In the embodiment of FIG. 9E, the signal transformation circuitry 124 eincludes a feedback loop for amplifier 952 in that at least some of thesignal output by the amplifier 952 is fed (through lines 953, filter954, and line 955) back to its input. This positive feedback increasesthe gain of the amplifier 952. The process of increasing the gain of anamplifying device by a feedback loop is sometimes called “regeneration”and, for this reason, it may be said that target device 950 performsregenerative amplification and/or includes a regenerative circuit. Theregenerative circuit comprises the amplifier 952 and its feedback loop,which includes filter 954, lines 953, and line 955. Using regenerativeamplification to increase the gain of the amplifier 952 ³ allows thetarget device 952 to include a single amplifier to achieve a desiredgain instead of using multiple amplifiers to achieve the same desiredgain. In this way, the amount of circuitry included in target device 950and the amount of power required to operate target device 950 may bereduced, which in turn decreases the cost of manufacturing target device950. ³ In the context of regeneration, the language “gain of theamplifier 952” is a shorthand for the gain induced to the signalsprovided (e.g., by receive antenna 122) to the regenerative circuit,which includes the amplifier 952 and its feedback loop. An increase inthe gain of the amplifier 952 refers to the gain achieved by using theregenerative circuit with the amplifier 952 relative to using amplifier952 without a feedback loop.

The filter 954, part of the feedback loop of amplifier 952, is used tocontrol the gain of the signal fed back to amplifier 952 (which gain issometimes referred to as loop gain) such that the circuit does notbecome unstable and oscillate out of control. Rather, filter 954provides sufficient loop gain control to stabilize the regenerativeamplification process while, at the same time, increasing the overallgain produced by the regenerative circuit. For example, in someembodiments, the feedback loop may be operated stably and allow for a 30dB gain increase in the gain of amplifier 952. In some instances, asmuch as a 50× increase in the gain of amplifier 952 may be achieved.

In some embodiments, additional components may be added to theregenerative circuit to further stabilize its operation while allowingfor an even greater increase of the gain produced by the regenerativecircuit. One such embodiment is illustrated in FIG. 9F, which shows atarget device 960 having signal transformation circuitry 124 f thatincludes quench control circuitry 958 in addition to the circuitry shownin and described with respect to FIG. 9E. Quench control circuitry 958may be configured to monitor the level of current in the regenerativecircuit and reduce the amount of power provided to amplifier 952 inorder to prevent the circuit from oscillating out of control. Theadditional gain control provided by quench control circuitry 958 (inaddition to the gain control provided by filter 954) may provide anadditional 10-20 dB of gain, in some embodiments, by allowing theregenerative circuit to behave closer to (but not at) a state ofout-of-control oscillation. As the introduction of quench controlcircuitry 958 allows for an even greater increase in the gain of theregenerative circuit, the resulting circuit (i.e., amplifier 952, itsfeedback loop through lines 953, filter 954, and line 955, and quenchcontrol circuit 958) may be termed a super-regenerative circuit.

In the embodiments of FIGS. 9E and 9F, amplifier 952 may be any suitabletype of amplifier, filter 954 may be any suitable type of filter, andfrequency multiplier 956 may be any suitable type of frequencymultiplier including any of the types described with reference tofrequency multiplier 908 shown in FIG. 9A. The target devices 950 and960 may be implemented in any suitable way. For example, in someembodiments, the target device 950 (or 960) may comprise a substratehaving the receive antenna 122 and transmit antenna 126 fabricatedthereon, and a semiconductor die mounted to the substrate, coupled tothe receive and transmit antennas, and having signal transformationcircuitry 124 e (or 1240 fabricated thereon.

As discussed herein, in some embodiments, one or more components of atarget device may be integrated circuits fabricated on a semiconductordie that is part of the target device. For example, the target devicemay comprise a substrate having one or more antennas coupled to thesubstrate and a semiconductor die, also coupled to the substrate, havingsignal transformation circuitry integrated therewith. However, in otherembodiments, a target device may be realized as a collection of discretecomponents coupled to a substrate (e.g., without implementing any of thecomponents as integrated circuitry). One such embodiment of a targetdevice is illustrated in FIGS. 9G and 9H, which show front and backviews of target device 970 implemented as a collection of discretecomponents on a printed circuit board. The front view of target device970 is shown next to a US quarter dollar coin to provide a sense of thesize of the target device.

Target device 970 comprises a circular polarized dual mode slot antenna987—the slots are on the back of the printed circuit board, as shown inFIG. 9H. As shown in FIG. 9G, RF signals received by antenna 987 areoutput to splitter 971, which outputs RF signals to filter 972. RFsignals filtered by filter 982 are provided to a low-noise amplifier973. RF signals output by the low-noise amplifier 973 are attenuated byattenuator 974 and, subsequently, amplified by amplifier 975. RF signalsoutput by amplifier 975 are attenuated by attenuator 976 and,subsequently, amplified by amplifier 977. RF signals output by amplifier977 are filtered by filter 978, attenuated by attenuator 979, and thenare provided to frequency multiplier 980. Frequency multiplier 980 isconfigured to receive input signals having a center frequency of f₀(e.g., 5 GHz) and generate output signals having a center frequency thatis 2f₀ (e.g., 10 GHz) thereby operating as a frequency doubler.

Next, RF signals output by frequency multiplier 980 are attenuated byattenuator 981 and, subsequently, amplified by amplifier 982. RF signalsamplified by amplifier 982 are filtered by filter 983, attenuated byattenuator 984, filtered by filter 985 and provided to splitter 986.Splitter 986 is coupled to dual mode slot antenna 987 and provides RFsignals to the dual mode slot antenna for transmission. Splitter 986splits the RF signals to generate two 90-degree out of phase RF signals(sometimes termed “in-phase” and “quadrature” signals) and providesthese signals to dual mode slot antenna 987.

As may be appreciated from the illustrative embodiments of a targetdevice described above, in some embodiments, a target device may have asingle dual band antenna configured to transmit and receive RF signalsat frequencies in different bands. Another illustrative example of atarget device having a dual band antenna is shown in FIG. 10, which is ablock diagram of target device 1000 comprising a substrate 1001 having asingle dual band antenna 1004 and circuitry 1002 disposed thereon.Circuitry 1002 includes frequency multiplier 1006 coupled to dual bandantenna 1004, bias control circuitry 1008 coupled to frequencymultiplier 1006, and auxiliary receiver 1010 coupled to bias controlcircuitry 1008. The frequency multiplier 1006 may be of any suitabletype including of any type described herein. Auxiliary receiver 1010 maybe of any suitable type and, for example, may be a ZigBee compatiblemodule such that the auxiliary receiver 1010 is configured tocommunicate according to one or more IEEE 802.15.4-based communicationprotocols.

In some embodiments, RF signals received on the receive channel of thedual band antenna 1004 are provided to frequency multiplier 1006 (e.g.,a 2× multiplier, a 3× multiplier, a 4× multiplier, an 8× multiplier,etc.) and, subsequent to being acted upon by the frequency multiplier1006, are transmitted using the transmit channel of the dual bandantenna 1004. For example, microwave RF signals having a first centerfrequency f₀ may be received on the receive channel of dual band antenna1004 and provided to frequency multiplier 1006, which may transform thereceived microwave RF signals to generate RF signals having a secondcenter frequency that is a harmonic of the first center frequency (e.g.,2f₀).

In some embodiments, the target device 1000 may be configured switchbetween the awake and sleep modes in response to a communicationreceived from an external device. For example, the auxiliary receiver1010 may be configured to receive, from an external device (e.g., acontroller), a communication indicating that the target device is to beturned off and, in response to the communication, cause the bias controlcircuitry 1008 to reverse bias the frequency multiplier 1006 so that thetarget device 1000 stops transmitting RF signals in response toreceiving RF signals. As another example, the auxiliary receiver 1010may be configured to receive, from an external device (e.g., acontroller), a communication indicating that the target device is to beturned on and, in response to the communication, cause the bias controlcircuitry 1008 to forward bias the frequency multiplier 1006 so that thetarget device 1000 begins to transmit RF signals in response toreceiving RF signals.

In some embodiments, bias control circuitry 1008 may be configured toapply a forward bias to frequency multiplier 1006 to increase the gainof the dual band antenna 1004 so as to increase the amplitude of the RFsignals transmitted by the dual band antenna 1004. For example, in someembodiments, the bias control circuitry 1008 may be configured to applya forward bias to the frequency multiplier 1006 so as to optimize theimpedance match between the dual band antenna 1004 and the frequencymultiplier 1006.

Target device 1000 may be manufactured in any suitable way. For example,in some embodiments, the target device 1000 may comprise a semiconductordie mounted to the substrate 1001 and at least some of the circuitry1002 may be integrated circuitry fabricated on the semiconductor die.For example, in some embodiments, the frequency multiplier 1006 and biascontrol circuitry 1008 may be fabricated on the semiconductor die. Asanother example, in some embodiments, the frequency multiplier 1006, thebias control circuitry 1008, and the auxiliary receiver 1010 may befabricated on the semiconductor die. In some embodiments, auxiliaryreceiver 1010 may be fabricated on substrate 1001, but not on thesemiconductor die. In some embodiments, the semiconductor die may beflip-chip bonded to the substrate 1001, which substrate may be a printedcircuit board, for example. In some embodiments, the substrate 1001 maycomprise one or more conductive layer and the dual band antenna may befabricated on the substrate by patterning the conductive layer(s).Although, in some embodiments, one or more portions target device 1000may be part of integrated circuitry fabricated on a semiconductor die,in other embodiments, the same portion(s) may be realized as discretecomponents on the substrate (e.g., as discrete components mounted on aPCB substrate).

As described with reference to FIGS. 9A-9H and 10, a target device maybe configured to receive RF signals having a first center frequency(e.g., 5 GHz or 60 GHz) and transmit RF signals having a second centerfrequency that is a harmonic of the first center frequency (e.g., 10 GHzor 120 GHz). It should be appreciated, however, that a target device isnot limited to transmitting RF signals at a single harmonic of thecenter frequency of the RF signals it receives. For example, in someembodiments, a target device may be configured to receive RF signalshaving a first center frequency (e.g., 5 GHz or 60 GHz) and transmit:(1) RF signals having a second center frequency (e.g., 10 GHz or 120GHz) that is a harmonic of the first center frequency; and (2) RFsignals having a third center frequency (e.g., 15 GHz or 180 GHz) thatis a harmonic of the first center frequency and is different from thesecond frequency. In some embodiments, the target device may be furtherconfigured to transmit RF signals having center frequencies at otherharmonic(s) of the first center frequency (e.g., 20 GHz or 240 GHz).

A target device that is configured to transmit RF signals at multipledifferent harmonics of a center frequency in response to receiving RFsignals having the center frequency may be called a “multi-spectraltarget device.” An interrogator device configured to transmit, to atarget device, RF signals having a center frequency and to receive, fromthe target device, RF signals at multiple different harmonics of thecenter frequency may be called a “multi-spectral interrogator device.” Amulti-spectral target device is not limited to responding with RFsignals only at harmonics of a center frequency of a received RF signaland, in some embodiments, may respond at multiple different frequencieseach of which depends on the center frequency in some way. For example,each of the multiple different frequencies may be: (1) a respectiveharmonic of the center frequency (as described with reference to FIG.11A); (2) offset from the center frequency by a respective amount;and/or (3) a respective harmonic of the sum of the center frequency andan offset frequency (e.g., as described with reference to FIG. 11B).Similarly, a multi-spectral interrogator may be configured to receive atany set of different frequencies that a corresponding multi-spectraltarget device is configured to emit.

The inventors have appreciated that using a system comprising one ormore multi-spectral interrogators configured to communicate with one ormore multi-spectral target devices may increase the accuracy with whichthe location of a multi-spectral target device (and/or multi-spectralinterrogator) may be determined. For example, when a multi-spectralinterrogator transmits, to a multi-spectral target device, an RF signalhaving a center frequency and receives, from a multi-spectral targetdevice, multiple RF signals at different harmonics of the centerfrequency, the overall bandwidth of the received RF signals received bythe interrogator is increased relative to the situation where a targetdevice transmits RF signals at only one harmonic of the centerfrequency. An increase in the bandwidth of the received RF signalsimproves the range resolution with which the multi-spectral device maybe located.

For example, an interrogator may transmit, to a target device, a chirphaving a center frequency of 61.25 GHz with its instantaneous frequencychanging linearly from 61 GHz to 61.5 GHz over its duration so that thebandwidth of the transmitted chirp is 500 MHz and may receive, from thetarget device, a responsive chirp having a center frequency of 122.5 GHzwith its instantaneous frequency changing linearly from 122 GHz to 123GHz over its duration so that the bandwidth of the received chirp is 1GHz. By contrast, when the interrogator transmits the same chirp to amulti-spectral target device, the interrogator may receive: (1) a firstresponsive chirp having a center frequency of 122.5 GHz and a bandwidthof 1 GHz; and (2) a second responsive chirp having a center frequency of245 GHz and a bandwidth of 2 GHz such that the total bandwidth of the RFsignals received by the interrogator is 3 GHz (unlike the 1 GHz of totalbandwidth when a multi-spectral target device is not used). Applyingphase-coherent processing to a received RF signal having a bandwidth of1 GHz may yield a range resolution of 15 cm. Increasing that bandwidthto 3 GHz may yield a range resolution of 5 cm, thereby providing athree-fold improvement in range resolution, thereby increasing theaccuracy with which the location of a target device may be determined.

The inventors have also recognized that having different multi-spectraltarget devices squawk at different combinations of harmonics of a centerfrequency may provide a way of determining which multi-spectral devicesare transmitting RF signals. For example, multi-spectral device A may beconfigured to receive RF signals having a center frequency (e.g., 5 GHz)and transmit responsive RF signals at the first and third harmonics ofthe center frequency (e.g., 10 GHz and 20 GHz). On the other hand,multi-spectral device B may be configured to receive RF signals havingthe same center frequency (e.g., 5 GHz) and transmit response RF signalsat the first and second harmonics of the center frequency (e.g., 10 GHzand 15 GHz). Thus, receiving an RF signal from a multi-spectral targetdevice having frequency content at 20 GHz may indicate thatmulti-spectral target device A transmitted the RF signal, whereasreceiving an RF signal from a multi-spectral device having frequencycontent at 15 GHz may indicate that multi-spectral target devicetransmitted the RF signal. More generally, different multi-spectraltarget devices may be configured to squawk at different combinations ofharmonics of a given center frequency thereby providing a way of“harmonically coding” their respective identities, which may facilitatedetermining which multi-spectral target device(s) are transmitting RFsignals at a given time. Additionally or alternatively, such harmoniccoding may be used to encode the angle and/or orientation of amulti-spectral target device relative to a multi-spectral interrogator.

FIG. 11A is a block diagram illustrating components of a multi-spectralinterrogator 1100 and a multi-spectral target device 1150, in accordancewith some embodiments of the technology described herein. Multi-spectralinterrogator 1100 comprises waveform generator 1102, amplifier 1106, andtransmit antenna 1108 configured to transmit RF signals generated bywaveform generator 1102 and amplified by amplifier 1106. The RF signalsgenerated by the waveform generator 1102 are also provided to powersplitter 1110 and, subsequently, to receive circuitry in theinterrogator configured to perform phase-coherent processing of the RFsignals transmitted by transmit antenna 1108 and RF signals received byreceive antennas 1120-1, 1120-2, . . . , 1120-n, where n is any suitableinteger greater than or equal to 3. The receive circuitry ofinterrogator 1100 comprises n different receive chains, one for each ofthe receive antennas 1120-1, 1120-2, . . . , 1120-n (or, more generally,a different receive chain for each different center frequency at whichthe target device 1150 transmits and the interrogator device 1100receives RF signals).

As shown in FIG. 11A, the receive circuitry of interrogator 1100includes a first receive chain including frequency multiplier 1112-1,amplifier 1114-1, filter 1116-1, and frequency mixer 1118-1, which isused for phase-coherent processing of RF signals received by antenna1120-1. The receive circuitry of interrogator 1100 further includes asecond receive chain including frequency multiplier 1112-2, amplifier1114-2, filter 1116-2, and frequency mixer 1118-2, which is used forphase-coherent processing of RF signals received by antenna 1120-2. Thereceive circuitry of interrogator 1100 further includes an nth receivechain including frequency multiplier 1112-n, amplifier 1114-n, filter1116-n, and frequency mixer 1118-n, which is used for phase-coherentprocessing of RF signals received by antenna 1120-n.

It should be appreciated that although in the illustrative embodiment ofFIG. 11A, the interrogator includes three or more receive antennas (and,consequently, three or more receive chains), in some embodiments, amulti-spectral interrogator may include two receive antennas and twoassociated receive chains (e.g., all the components of interrogator 1100whose labels end with “-1” and “-2,” but not those components whoselabels end with “-n.” Additionally, although there are “n” separatereceive antennas shown as being part of interrogator 1100, that numberof receive antennas may be reduced by combining at least some of thereceive antennas (e.g. two receive antennas) into a single receiveantenna using a multiplexer (e.g., duplexer). This may reduce the sizeof the interrogator.

Multi-spectral target device 1150 comprises receive antenna 1152configured to receive RF signals at a first center frequency andmultiple transmit antennas 1160-1, 1160-2, and 1160-n, configured totransmit RF signals at respective harmonics of the first centerfrequency. The RF signals received by receive antenna 1152 are providedto signal transformation circuitry configured to generate RF signalshaving as center frequencies different harmonics of the first centerfrequency. The signal transformation circuitry includes a respectivesignal transformation chain for each harmonic of the first centerfrequency at which the multi-spectral target device is configured totransmit RF signals.

As shown in FIG. 11A, the signal transformation circuitry ofmulti-spectral target device 1150 includes a first signal transformationchain including frequency multiplier 1154-1, amplifier 1156-1, andfilter 1158-1. The signal transformation circuitry of multi-spectraltarget device 1150 further includes a second signal transformation chainincluding frequency multiplier 1154-2, amplifier 1156-2, and filter1158-2. The signal transformation circuitry of multi-spectral targetdevice 1150 further includes an nth signal transformation chainincluding frequency multiplier 1154-n, amplifier 1156-n, and filter1158-n.

In some embodiments, each of the frequency multipliers 1154-1, 1154-2,and 1154-n may be configured to increase the frequencies in the receivedRF signals by different amounts. For example, the frequency multipliers1154-1, 1154-2, and 1154-n may increase the frequencies by a factor oftwo, three, and four respectively. As a specific example, RF signalsreceived by antenna 1152 having a center frequency of 60 GHz may beprovided to frequency multipliers 1154-1, 1154-2, and 1154-n, which maygenerate RF signals having center frequencies of 120 GHz, 180 GHz, and240 GHz, respectively. In this example, transmit antenna 1160-1 wouldtransmit RF signals having a center frequency of 120 GHz, transmitantenna 1160-2 would transmit RF signals having a center frequency of180 GHz, and transmit antenna 1160-n would transmit RF signals having acenter frequency of 240 GHz. Each of frequency multipliers 1154-1,1154-2, . . . , 1154-n may be implemented in any suitable way describedherein including, for example, as a series of frequency multipliers. Inthis way, a higher-order frequency multiplier (e.g., a 4× frequencymultiplier) may be implemented a single frequency multiplier (e.g., a 4×multiplier) or as a series of lower-order frequency multipliers (e.g.,two 2× multipliers).

It should be appreciated that although in the illustrative embodiment ofFIG. 11A, the target device includes three or more transmit antennas(and, consequently, three or more signal transformation chains), in someembodiments, a multi-spectral target device may include only twotransmit antennas and two signal transformation chains (e.g., all thecomponents of target device 1150 whose labels end with “-1” and “-2,”but not those components whose labels end with “-n.” Additionally,although there are “n” separate transmit antennas shown as being part oftarget device 1150, that number of transmit antennas may be reduced bycombining at least some of the transmit antennas (e.g., two transmitantennas) into a single transmit antenna using a multiplexer (e.g.,duplexer). This may reduce the size of the target device.

To further explain aspects of how the multi-spectral interrogator 1100and target device 1150 operate, consider embodiments where n=3 such thatthe interrogator 1100 has three receive antennas and target device 1150has three transmit antennas. In such embodiments, multi-spectralinterrogator 1100 may transmit, to multi-spectral target device 1150, afirst RF signal having a first center frequency (e.g., 60 GHz) usingtransmit antenna 1108. Multi-spectral target device may receive thefirst RF signal using receive antenna 1152 and generate: (1) a second RFsignal having a second center frequency (e.g., 120 GHz) using frequencymultiplier 1154-1, amplifier 1156-1, and filter 1158-1; (2) a third RFsignal having a third center frequency (e.g., 180 GHz) different fromthe first and second center frequencies using frequency multiplier1154-2, amplifier 1156-2, and filter 1158-2; and (3) a fourth RF signalhaving a fourth center frequency (e.g., 240 GHz) different from thefirst, second, and third center frequencies) using frequency multiplier1154-n, amplifier 1156-n, and filter 1158-n. In turn, the second, third,and fourth RF signals are transmitted by transmit antennas 1160-1,1160-2, and 1160-n, respectively.

In turn, interrogator 1100 may receive the second RF signal having thesecond center frequency (e.g., 120 GHz) using receive antenna 1120-1 andprovide it to frequency mixer 1118-1 for mixing with a transformedsignal obtained by transforming the first RF signal using frequencymultiplier 1112-1, amplifier 1114-1, and filter 1116-1 and having thesecond center frequency. The frequency mixer 1118-1 may output a firstmixed RF signal indicative of the distance between the interrogator 1100and target device 1150. The interrogator 1100 may further receive thethird RF signal having the third center frequency (e.g., 180 GHz) usingreceive antenna 1120-2 and provide it to frequency mixer 1118-2 formixing with a transformed signal obtained by transforming the first RFsignal using frequency multiplier 1112-2, amplifier 1114-2, and filter1116-2 and having the third center frequency. The frequency mixer 1118-2may output a second mixed RF signal indicative of the distance betweenthe interrogator 1100 and target device 1150. The interrogator 1100 mayfurther receive the fourth RF signal having the fourth center frequency(e.g., 240 GHz) using receive antenna 1120-n and provide it to frequencymixer 1118-n for mixing with a transformed signal obtained bytransforming the first RF signal using frequency multiplier 1112-n,amplifier 1114-n, and filter 1116-n and having the fourth centerfrequency. The frequency mixer 1118-n may output a third mixed RF signalindicative of the distance between the interrogator 1100 and targetdevice 1150.

Next the first, second, and third mixed RF signals generated byfrequency mixers 1118-1, 1118-2, and 1118-n may be processed (e.g.,using a processor not shown in FIG. 11A, but which may be in or externalto interrogator 1100) to determine the distance between the interrogator1100 and target device 1150. This may be done in any suitable way. Forexample, in some embodiments, the first, second and third mixed RFsignals may be combined to generate a single RF signal indicative of thedistance between the interrogator 1100 and target device 1150. In someembodiments, the mixed RF signals may be combined in the frequencydomain. For example, the mixed RF signals may be apodized (e.g.,windowed with a suitable windowing function) and added to one another inthe frequency domain to generate the combined signal. As anotherexample, the mixed RF signals may be used to estimate a combined RFsignal using bandwidth extension techniques. Any of the foregoingcombination techniques may be implemented in the time-domain and/or inthe frequency domain. Regardless of how the mixed RF signals arecombined to generate a combine RF signal, the combined RF signal may beused to determine the distance between the interrogator 1100 and targetdevice 1150. This may be done by performing an inverse Fourier transformon the combined RF signal and identifying the location of the peak,which location indicates the time of flight between interrogator 1100and target device 1150, and convert the location of the peak to anestimate of the distance between the interrogator and target device, orin any other suitable way.

Multi-spectral interrogator 1100 may be manufactured in any suitableway. For example, in some embodiments, the interrogator 1100 maycomprise a substrate having the transmit antenna 1108 and receiveantennas 1120-1, 1120-2, and 1120-n fabricated thereon. For example thesubstrate may comprise one or more conductive layers and the transmitand receive antennas may be patterned in the conductive layer(s). Insome embodiments, the interrogator device may comprise a semiconductordie mounted on the substrate and the receive circuitry (e.g., frequencymultipliers 1112-1, 1112-2, 1112-n, amplifiers 1114-1, 1114-2, . . . ,1114-n, filters 1116-1, 1116-2, . . . , 1116-n, and frequencymultipliers 1118-1, 1118-2, . . . , 1118-n) may be integrated circuitryfabricated on the semiconductor die. In some embodiments, transmitcircuitry including waveform generator 1102 and amplifier 1106 may alsobe integrated circuitry fabricated on the semiconductor die. In someembodiments, waveform generator may be at least partially or fully offthe semiconductor die but on the substrate. Although, in someembodiments, one or more portions of the interrogator 1100 may be partof integrated circuitry fabricated on a semiconductor die, in otherembodiments, the same portion(s) may be realized as discrete componentson the substrate (e.g., as discrete components mounted on a PCBsubstrate).

Multi-spectral target device 1150 may be manufactured in any suitableway. For example, in some embodiments, the target device may comprise asubstrate having the receive antenna 1152 and transmit antennas 1160-1,1160-2, and 1160-n fabricated thereon. For example the substrate maycomprise one or more conductive layers and the transmit and receiveantennas may be patterned in the conductive layer(s). In someembodiments, the target device may comprise a semiconductor die mountedon the substrate and the signal transformation circuitry (e.g.,frequency multipliers 1154-1, 1154-2, 1154-n, amplifiers 1156-1, 1156-2,. . . , 1156-n, and filters 1158-1, 1158-2, . . . , 1158-n) may beintegrated circuitry fabricated on the semiconductor die. Although, insome embodiments, one or more portions of the target device 1150 may bepart of integrated circuitry fabricated on a semiconductor die, in otherembodiments, the same portion(s) may be realized as discrete componentson the substrate (e.g., as discrete components mounted on a PCBsubstrate).

FIG. 11B is a block diagram illustrating components multi-spectralinterrogator 1170 and multi-spectral target device 1185, in accordancewith some embodiments of the technology described herein. In theembodiment illustrated in FIG. 11B, the interrogator 1170 transmits twodifferent RF signals to target device: (1) a first RF signal generatedat least in part by using waveform generator 1171 (this signal isanalogous to the signal transmitted by interrogator 1100 described withreference to FIG. 11A); and (2) a second RF signal generated by localoscillator 1174 (this has no counterpart in the embodiment of FIG. 11A).After being received by the target device, this second RF signal (afterany suitable amplification and/or frequency multiplication) may be mixedwith the first RF signal to shift the first RF signal by a desiredamount to obtain a frequency-shifted RF signal. In turn, thefrequency-shifted RF signal may be frequency multiplied by any suitablefactors to generate RF signals to transmit back to interrogator device1170. This configuration is described in greater detail below.

Multi-spectral interrogator 1170 comprises waveform generator 1171,power splitter 1172 a, and transmit antenna 1173 configured to transmitRF signals generated by the waveform generator 1171. Interrogator 1170further comprises oscillator 1174, power splitter 1172 b, and transmitantenna 1175 configured to transmit RF signals (e.g., continuous wavesignals) generated by oscillator 1174. The RF signals generated bywaveform generator 1171 and oscillator 1174 are also provided to receivecircuitry in interrogator 1170 configured to perform phase-coherentprocessing of the RF signals transmitted by transmit antennas 1173 and1175, and RF signals received by receive antennas 1176-1, 1176-2, . . ., 1176-n, where n is any suitable integer greater than or equal to 3.The receive circuitry of interrogator 1170 comprises n different receivechains, one for each of the receive antennas 1176-1, 1176-2, . . . ,1176-n (or, more generally, a different receive chain for each differentcenter frequency at which the target device 1185 transmits and theinterrogator device 1170 receives RF signals).

As shown in FIG. 11B, the receive circuitry of interrogator 1170includes a first receive chain including frequency multipliers 1179-1and 1183-1, amplifiers 1177-1 and 1180-1, and frequency mixers 1178-1and 1182-1, which receive chain is used for phase-coherent processing ofRF signals received by antenna 1176-1. The receive circuitry ofinterrogator 1170 further includes a second receive chain includingfrequency multipliers 1179-2 and 1183-2, amplifiers 1177-2 and 1180-2,and frequency mixers 1178-2 and 1182-2, which receive chain is used forphase-coherent processing of RF signals received by antenna 1176-2. Thereceive circuitry of interrogator 1170 further includes an nth receivechain including frequency multipliers 1179-n and 1183-n, amplifiers1177-n and 1180-n, and frequency mixers 1178-n and 1182-n, which receivechain is used for phase-coherent processing of RF signals received byantenna 1176-n.

Although in the illustrative embodiment of FIG. 11B, the interrogator1170 includes three or more receive antennas (and, consequently, threeor more receive chains), in some embodiments, a multi-spectralinterrogator may include two receive antennas and two associated receivechains (e.g., all the components of interrogator 1100 whose labels endwith “-1” and “-2,” but not those components whose labels end with “-n.”Additionally, although there are “n” separate receive antennas shown asbeing part of interrogator 1170, that number of receive antennas may bereduced by combining at least some of the receive antennas (e.g. tworeceive antennas) into a single receive antenna using a multiplexer(e.g., duplexer). This may reduce the size of the interrogator.

Multi-spectral target device 1185 comprises receive antenna 1186configured to receive RF signals at a first center frequency f₁ (e.g.,chirps generated by waveform generator 1171 transmitted by transmitantenna 1173) and receive antenna 1188 configured to receive RF signalshaving a second center frequency f₂ (e.g., a continuous wave signalsgenerated by oscillator 1174 and transmitted by transmit antenna 1175).Target device 1185 further comprises amplifiers 1187, amplifier 1189,frequency multiplier 1190 and frequency mixer 1191. The frequency mixer1191 is configured to mix RF signals received by antenna 1186 andamplified by amplifier 1187 with RF signals received by antenna 1188,amplified by amplifier 1189 and frequency multiplied by frequencymultiplier 1190 to obtain frequency shifted RF signals having a thirdcenter frequency f₃ (which may be given by f₃=f₁+kf₂, where k is themultiplicative factor induced by frequency multiplier 1190). Targetdevice 1185 further comprises multiple transmit antennas 1196-1, 1196-2,and 1196-n, configured to transmit RF signals at respective harmonics ofthe third center frequency (e.g., 2f₃, 3f₃, etc.). The frequency-shiftedRF signals output by frequency mixer 1191 and having the third centerfrequency are filtered by filter 1192, amplified by amplifier 1193, andprovided to signal transformation circuitry configured to generate RFsignals having as center frequencies different harmonics of the thirdcenter frequency. The signal transformation circuitry includes arespective signal transformation chain for each harmonic of the thirdcenter frequency at which the target device 1185 is configured totransmit RF signals.

As shown in FIG. 11B, the signal transformation circuitry of targetdevice 1185 includes a first signal transformation chain includingfrequency multiplier 1194-1 and filter 1195-1, a second signaltransformation chain including frequency multiplier 1194-2, and filter1195-2, and an nth chain including frequency multiplier 1194-n andfilter 1195-n.

It should be appreciated that although in the illustrative embodiment ofFIG. 11B, the target device 1185 includes three or more transmitantennas (and, consequently, three or more signal transformationchains), in some embodiments, a multi-spectral target device may includeonly two transmit antennas and two signal transformation chains (e.g.,all the components of target device 1150 whose labels end with “-1” and“-2,” but not those components whose labels end with “-n.” Additionally,although there are “n” separate transmit antennas shown as being part oftarget device 1150, that number of transmit antennas may be reduced bycombining at least some of the transmit antennas (e.g., two transmitantennas) into a single transmit antenna using a multiplexer (e.g.,duplexer). This may reduce the size of the target device.

To further explain aspects of how the interrogator 1170 and targetdevice 1185 operate, consider embodiments where n=3 such that theinterrogator 1170 has three receive antennas and target device 1185 hasthree transmit antennas. In such embodiments, interrogator 1170 maytransmit, to target device 1185, a first RF signal having a first centerfrequency (e.g., 40 GHz) using transmit antenna 1173 and a second RFsignal having a second center frequency (e.g., 10 GHz) using transmitantenna 1175. Target device 1185 may receive the first RF signal usingantenna 1186, amplify it using amplifier 1187, and provide the result asa first input to frequency mixer 1191. Target device 1185 may alsoreceive the second RF signal using antenna 1188, amplify it usingamplifier 1189, and increase the frequency in the resulting signal by afactor of two using frequency multiplier 1190 to obtain an RF signalhaving a center frequency twice that of the second center frequency(e.g., 20 GHz), and provide the result as a second input to frequencymixer 1191. Based on these inputs, frequency mixer 1191 may beconfigured to generate a third RF signal having a third center frequency(60 GHz). Target device 1185 may then use the third RF signal togenerate: (1) a fourth RF signal having a fourth center frequency (e.g.,120 GHz) at least by using frequency multiplier 1194-1; (2) a fifth RFsignal having a fifth center frequency (e.g., 180 GHz) at least by usingfrequency multiplier 1194-2; and (3) a sixth RF signal having a sixthcenter frequency (e.g., 240 GHz) at least by using frequency multiplier1194. The fourth, fifth, and sixth RF signals are subsequentlytransmitted by transmit antennas 1196-1, 1196-2, and 1196-n,respectively.

In turn, interrogator 1170 may receive the fourth RF signal having thefourth center frequency (e.g., 120 GHz) using receive antenna 1176-1,amplify it using amplifier 1177-1, and provide it as an input tofrequency mixer 1178-1 for mixing with a transformed signal obtained bytransforming the second RF signal using frequency multiplier 1179-1. Theoutput of frequency mixer 1178-1 is amplified by amplifier 1180-1 andprovided as an input to frequency mixer 1181-1 for mixing with atransformed signal obtained by transforming the first RF signal usingfrequency multiplier 1183-1. The frequency mixer 1181-1 outputs, on line1182-1, a first mixed RF signal indicative of the distance between theinterrogator 1170 and target device 1185. The interrogator 1170 may alsoreceive the fifth RF signal having the fifth center frequency (e.g., 180GHz) using receive antenna 1176-2, amplify it using amplifier 1177-2,and provide it as an input to frequency mixer 1178-2 for mixing with atransformed signal obtained by transforming the second RF signal usingfrequency multiplier 1179-2. The output of frequency mixer 1178-2 isamplified by amplifier 1180-2 and provided as an input to frequencymixer 1181-2 for mixing with a transformed signal obtained bytransforming the first RF signal using frequency multiplier 1183-2. Thefrequency mixer 1181-2 outputs, on line 1182-2, a second mixed RF signalindicative of the distance between the interrogator 1170 and targetdevice 1185. The interrogator 1170 may also receive the sixth RF signalhaving the sixth center frequency (e.g., 240 GHz) using receive antenna1176-n, amplify it using amplifier 1177-n, and provide it as an input tofrequency mixer 1178-n for mixing with a transformed signal obtained bytransforming the second RF signal using frequency multiplier 1179-n. Theoutput of frequency mixer 1178-n is amplified by amplifier 1180-n andprovided as an input to frequency mixer 1181-n for mixing with atransformed signal obtained by transforming the first RF signal usingfrequency multiplier 1183-n. The frequency mixer 1181-n outputs, on line1182-n, a second mixed RF signal indicative of the distance between theinterrogator 1170 and target device 1185.

Next the first, second, and third mixed RF signals generated byfrequency mixers 1181-1, 1181-2, and 1181-n may be processed (e.g.,using a processor not shown in FIG. 11B, but which may be in or externalto interrogator 1170) to determine the distance between the interrogator1170 and target device 1185. This may be done in any suitable wayincluding in any of the ways described above with reference to FIG. 11A.

Multi-spectral interrogator 1170 may be manufactured in any suitableway. For example, in some embodiments, the interrogator 1170 maycomprise a substrate having the transmit antennas 1173 and 1175, andreceive antennas 1176-1, 1176-2, and 1176-n fabricated thereon. Forexample the substrate may comprise one or more conductive layers and thetransmit and receive antennas may be patterned in the conductivelayer(s). In some embodiments, the interrogator may comprise asemiconductor die mounted on the substrate and the receive circuitry(e.g., the frequency multipliers, frequency mixers, and amplifiers shownas part of interrogator 1170) may be integrated circuitry fabricated onthe semiconductor die. In some embodiments, waveform generator 1171 andoscillator 1174 may also be integrated circuitry fabricated on thesemiconductor die, but in other embodiments one or both of waveformgenerator 1171 and oscillator 1174 may be realized as discretecomponents on the substrate (e.g., as discrete components mounted on aPCB substrate).

Similarly, target device 1150 may be manufactured in any suitable way.In some embodiments, the target device may comprise a substrate havingthe receive antennas 1186 and 1188, and transmit antennas 1196-1,1196-2, and 1196-n fabricated thereon. For example the substrate maycomprise one or more conductive layers and the transmit and receiveantennas may be patterned in the conductive layer(s). In someembodiments, the target device may comprise a semiconductor die mountedon the substrate and the signal transformation circuitry (e.g., thefrequency multipliers, frequency mixers, filters, and amplifiers shownas part of target device 1185) may be integrated circuitry fabricated onthe semiconductor die. Although, in some embodiments, one or moreportions of the target device 1185 may be part of integrated circuitryfabricated on a semiconductor die, in other embodiments, the sameportion(s) may be realized as discrete components on the substrate(e.g., as discrete components mounted on a PCB substrate).

It should be appreciated that the embodiments of multi-spectralinterrogators and target devices shown in FIGS. 11A and 11B areillustrative and that there are variations. For example, in someembodiments, there may be zero, one, two, three, or any other suitablenumber of amplifiers of any suitable type between any pair of circuitsshown in FIGS. 11A and 11B. As another example, there may be zero, one,two, three, or any other suitable number of filters of any suitable typebetween any pair of circuits shown in FIGS. 11A and 11B. As yet anotherexample, the target device 1185 may be implemented without frequencymultiplier 1190, in some embodiments. It should also be appreciated thatany of the amplifiers, frequency mixers, frequency multipliers, andfilters shown in FIGS. 11A and 11 b may be of any suitable type and maybe implemented in any suitable way, as aspects of the technologydescribed herein are not limited in this respect. Additionally, itshould be appreciated that each of waveform generators 1102 and 1171 maybe configured to generate RF signals of any suitable type including anyof the types described herein with reference to waveform generator 110.

As discussed herein including with reference to FIG. 9C, in someembodiments, a target device may include a local oscillator configuredto generate a signal having a fixed frequency used to offset thefrequencies in RF signals received from an interrogator device as partof generating RF signals to transmit back to the interrogator device.For example, in some embodiments, a target device may include: (1) anoscillator configured to generate a first RF signal having a firstcenter frequency f₁ (the first RF signal may be a continuous wave signalhaving a fixed frequency to be used as an offset frequency); (2) areceive antenna configured to receive, from an interrogator, a second RFsignal having a second center frequency f₂ (the second RF signal may bea chirp, for example); and (3) a frequency mixer configured to mix thefirst RF signal with the second RF signal to obtain a third RF signalhaving a third center frequency f₃ (e.g., where f₃=f₂±f₁). The targetdevice may further include a transmit antenna configured to transmit thethird RF signal to the interrogator device.

In some embodiments, such a target device architecture may be realizedusing an antenna disposed on a semiconductor substrate. For example, insome embodiments, a target device may comprise: (1) a substrate; (2) anoscillator disposed on the substrate and configured to generate a firstRF signal having a first center frequency; (3) a dual band antennamounted on the substrate and configured to receive a second RF signalhaving a second center frequency from an interrogator; and (4) afrequency mixer configured to generate a third RF signal by mixing thefirst RF signal with the second RF signal and provide the generatedthird RF signal to the dual band antenna for transmission back to theinterrogator device. In some embodiments, the substrate may be asemiconductor substrate, the dual band antenna may be amicroelectromechanical system (MEMS) antenna mounted on thesemiconductor substrate, and the frequency mixer may be mounted on thedual band antenna.

FIG. 12A is a diagram of an illustrative target device 1200 comprising asubstrate 1202, an oscillator 1204 disposed on the substrate 1202; adual band antenna 1206 mounted on the substrate 1202 using posts 1205;and frequency mixer 1208 disposed on dual band antenna 1206. In someembodiments, the frequency mixer 1208 comprises (e.g., consists of) asingle transistor or a single diode. The oscillator 1204 may beelectromagnetically coupled to frequency mixer 1208. For example, in theillustrated embodiment of FIG. 12A, oscillator 1204 is located on thesubstrate at a location below the dual band antenna and, thereby, isconfigured to generate RF signals and radiate them at frequency mixer1208, which is disposed on the dual band antenna 1206.

In embodiments where, the frequency mixer 1208 comprises or consists ofa single diode, the frequency mixer 1208 may be a Schottky diode, asilicon diode, a varistor-type diode frequency multiplier, avaractor-type frequency multiplier, a step recover diode frequencymultiplier, or a PIN diode frequency multiplier, any (e.g., all) ofwhich may or may not be biased with a quiescent bias current.

In some embodiments, oscillator 1204 may be configured to generate afirst RF signal having a first frequency and radiate the first RF signalinto the dual band antenna 1206. The frequency mixer 1208 may beconfigured to mix the first RF signal, generated by the oscillator 1204,with a second RF signal having a second center frequency and received bythe dual band antenna from an interrogator device to obtain, as theoutput of frequency mixer 1208, a third RF signal having a third centerfrequency (which may be the sum or difference of the first and secondcenter frequencies). In turn, the RF signal output by the frequencymixer 1208 may be transmitted by the dual band antenna, for example, tothe interrogator device.

In some embodiments, the substrate 1202 may be a semiconductor substrateand, for example, may be a semiconductor die. The semiconductor die maybe a silicon die, for instance from a bulk silicon wafer orsilicon-on-insulator (SOI) wafer. In some embodiments, the die may be asingle crystal silicon die. In some embodiments, the die may be a CMOSdie, a BiCMOS die, a GaAs die, a GaN die, or may be formed of any othersemiconductor material.

In some embodiments, the oscillator 1204 may be a cavity resonatorformed within the substrate (e.g., within a semiconductor die), a planarmicrowave oscillator, or any other suitable type of oscillator. As shownin the illustrative embodiment of FIG. 12A, the oscillator 1204 islocated on the substrate 1202 at a location underneath the dual bandantenna 1206. In other embodiments, however, the oscillator 1204 may belocated at a location that is not beneath the dual band antenna 1206. Insuch embodiments, the oscillator 1204 may be coupled, via a feed line,to a coupling device disposed on the substrate at a location underneaththe dual band antenna 1206. This is one example of how the oscillator1204 may be electromagnetically coupled to frequency mixer 1208 withoutbeing located directly underneath the dual band antenna 1206 on whichthe frequency mixer 1208 is located.

In some embodiments, the dual mode antenna 1206 may be a MEMS antenna.For example, in embodiments where the dual mode antenna 1206 isconfigured to receive RF signals in a range of 50-70 GHz and transmit RFsignals in a range of 100-140 GHz, the dual mode antenna may be realizedas a MEMS antenna. The MEMS antenna may be fabricated on thesemiconductor substrate 1202 using any suitable semiconductorfabrication process(es) (e.g., deposition, etching, lithography,patterning, etc.). It should be appreciated, however, that the dual modeantenna 1206 is not limited to being a MEMS antenna and may be a largerphysical structure, manufactured separately from the substrate 1202, asthe case may be in embodiments where the dual mode antenna is configuredto receive/transmit RF signals at lower frequencies (requiring largerwavelengths and, therefore, a larger antenna). For example, in someembodiments, a dual band antenna configured to receive RF signals in arange of 4-6 GHz and transmit RF signals in a range of 8-12 GHz may bemanufactured separately from the substrate 1202 (e.g., without usingsemiconductor fabrication techniques) and subsequently be mounted onsubstrate 1202. Such an antenna may be fabricated from any suitablematerial such as, for example, aluminum or brass. In some embodiments,the dual band antenna may be a patch antenna and/or a planar antenna.

As shown in FIG. 12A, the dual band antenna 1206 is mounted on substrate1202 using four posts 1205. However, it should be appreciated that thedual band antenna 1206 may be mounted on substrate 1202 using anysuitable number of posts (e.g., 2, 3, 5, etc.) or any other suitablesupport structure(s), as aspects of the technology described herein arenot limited in this respect. In embodiments where the dual band antenna1206 is a MEMS antenna, the posts 1205 may be manufactured using anysuitable semiconductor fabrication technique(s).

Additionally, as shown in FIG. 12A, target device 1200 further comprisesbias control circuitry 1212 disposed on substrate 1202 and electricallycoupled to frequency mixer 1208 using line 1210. In the illustratedembodiment, line 1210 runs along substrate 1202 from bias controlcircuitry 1212 to one of the posts 1205, up along the post 1205, andthen along dual band antenna 1206 to the frequency mixer 1208. It shouldbe appreciated, however, that bias control circuitry 1212 may beelectrically coupled to frequency mixer 1208 in any other suitable way,as aspects of the technology described herein are not limited in thisrespect. For example, in some embodiments, line 1210 may transition fromsubstrate 1202 to antenna 1206 using its own dedicated post, separatefrom posts 1205.

The bias control circuitry 1212 may be configured to perform one or morefunction analogous to those of bias control circuitry 1008 describedwith reference to FIG. 10. For example, the bias control circuitry 1212may be configured to reverse bias the frequency mixer 1208 to turn thetarget device 1200 off (e.g., so that the target device 1200 stopstransmitting RF signals in response to receiving RF signals). In someembodiments, bias control circuitry 1212 may be configured to apply aforward bias to frequency mixer 1208 to increase the gain of the dualband antenna 1206 so as to increase the amplitude of the RF signalstransmitted by the dual band antenna 1206. For example, in someembodiments, the bias control circuitry 1212 may be configured to applya forward bias to the frequency mixer 1208 so as to optimize theimpedance match between the dual band antenna 1206 and the frequencymixer 1208.

FIG. 12B is a diagram of a side view of a target device 1200 in anembodiments, where the oscillator 1204 is realized as a cavity resonator1207, dual band antenna 1206 is a MEMS antenna, and frequency mixer 1208is realized as a P or N doped square 1214 disposed on the MEMS antenna1206. Cavity resonator 1207 is configured to generate RF signals andtransmit them to dual band antenna 1206 through air gap. In thisconfiguration, the dual band antenna 1206 may be efficient

It should be appreciated that the embodiments illustrated in FIGS. 12Aand 12B are illustrative and that there are variations. For example, insome embodiments, target device 1200 may further comprise circuitry foramplifying RF signals after they are received by dual band antenna 1206and/or before RF signals are to be transmitted by dual band antenna1206. For example, in some embodiments, the target device may comprise asingle-stage transistor operating as both a frequency mixer and as anamplifier. The input of the single-stage transistor may be impedancetuned via the receive mode of the dual band antenna 1206 and the outputof the single-stage transistor may be impedance tuned via the transmitmode of the dual band antenna 1206.

As discussed herein, in some embodiments, a localization system maycomprise multiple interrogator devices configured to interrogate one ormore target devices in order to determine the location(s) of the targetdevice(s) based on their respective responses to the interrogating RFsignals. In some embodiments, each of the multiple interrogator devicesmay be configured to transmit RF signals to a target device and receiveresponsive RF signals from the target device. However, in otherembodiments, only one of the interrogator devices may interrogate thetarget devices by transmitting RF signals to the target device, whileall the interrogator devices (including the transmitting interrogator)may “listen” by receiving RF signals generated by the target device inresponse to receiving RF signals from the transmitting interrogator. Thetransmitting interrogator device may be referred herein to as a “master”interrogator device. The “listening” interrogator devices may bereferred to herein as “slave” interrogator devices.

In some embodiments, a slave interrogator device may not include atransmit antenna for transmitting RF signals to a target device nortransmit circuitry for generating RF signals for transmission. This mayreduce the cost of manufacturing, the size, and the power consumption ofthe slave interrogator relative to an interrogator device that performsboth transmit and receive functions. For example, the size of areceive-only interrogator die substrate may be reduced because it doesnot need to accommodate a transmit antenna. As another example, the sizeof the semiconductor die in the receive-only interrogator may be reducedbecause it does not need to include transmit circuitry.

In some embodiments, the master interrogator and one or more slaveinterrogators may be phase coherent with one another. In someembodiments, phase coherence among the master and slave interrogatorsmay be achieved by using synchronization circuitry to provide all theoscillators a common reference signal (e.g., a chirped direct digitallysynthesized reference signal or a signal generated by fixed-frequencyreference oscillator). The common reference signal may embody RF signalsynthesis information that each of the slave interrogators may utilizefor generating a respective local version of the RF signal transmittedto the target device by the master interrogator. In turn, at aparticular slave interrogator, the local version of the RF signaltransmitted to the target device by the master interrogator may beprocessed phase coherently with the RF signal received by the slaveinterrogator from the target device. In this way, each slaveinterrogators may determine a distance (or at least generate a mixed RFsignal indicative of the distance) between the slave interrogator andthe target device.

FIG. 14A is a block diagram of an illustrative localization system 1400comprising multiple synchronized (e.g., phase coherent) interrogatorsincluding master interrogator 1402 and three receive-only interrogators1404, 1406, 1408. Although there are three receive-only interrogatorsshown in the illustrative embodiment of FIG. 14A, in other embodiments,a localization system may include any suitable number (e.g., one, two,four, five, six, seven, eight, nine, ten, etc.) of receive-onlyinterrogators synchronized with master interrogator 1402. In addition,although in the illustrated embodiment of FIG. 14A each of theinterrogators 1404, 1406, and 1408 is a receive-only interrogator, inother embodiments, any of the interrogators 1404, 1406, and 1408 may becapable of transmitting and receiving RF signals, but may be configuredto operate in a receive-only mode.

The system 1400 further includes synchronization circuitry comprisingfixed-frequency reference oscillator 1410 and lines 1412 configured toprovide output of oscillator 1410 to each of the interrogators 1402,1404, 1406, and 1408. The master interrogator 1402 may be of anysuitable type including any of the types interrogators described herein.Each of interrogators 1404, 1406, and 1408, may be of any suitable typeincluding the type described below with reference to FIG. 14C.

As shown in FIG. 14A, the system 1400 also includes trigger lines 1414,which help to ensure that each of the receive-only interrogators 1404,1406, and 1408 generates, at the same time, a local version of the RFsignal transmitted by the master interrogator 1402. This local versionof the transmitted RF signal will be used to generate a local signal formixing with a received RF signal from the target device that wasgenerated by the target device in response to receiving the RF signaltransmitted by the master interrogator 1402. When the RF signalsinvolved are chirps, the trigger lines 1414 may be said to allow thereceive-only interrogators to “receive-chirp” at the same time.Accordingly, in some embodiments, the master interrogator 1402 may beconfigured to share a trigger signal with receive-only interrogators1404, 1406, and 1408 using trigger lines 1414. The master interrogator1402 may be configured to transmit and receive RF signals at a risingedge of the trigger signal, and each of the receive-only interrogators1404, 1406, and 1408 may generate their local versions of the RF signaltransmitted by interrogator 1402 and receive an RF signal from thetarget device at the rising edge of the same trigger. For example, themaster interrogator 1402 may be configured to transmit and receivechirps at a rising edge of the trigger signal, and each of thereceive-only interrogators 1404, 1406, and 1408 may generate their localversions of the transmitted chirp and receive a chirp from the targetdevice at the rising edge of the same trigger.

In some embodiments, any one (e.g., all) of the receive-onlyinterrogators 1404, 1406, and 1406 may be configured to generateinformation indicative of the distance between the interrogator and thetarget device. A receive-only interrogator may provide the generatedinformation to the master interrogator 1402 via data lines 1414. Forexample, in some embodiments, each receive-only interrogator may beconfigured to determine an estimate of the distance for an RF signalbetween itself and the target device and provide the determined estimateto master interrogator 1402. Based on the provided estimates, the masterinterrogator 1402 may determine a location of the target device and mayinclude circuitry (e.g., a processor) for performing such adetermination.

As another example, in some embodiments, a receive-only interrogator mayobtain information indicative of the distance between the receiveinterrogator and the target device, but may not be configured tocomplete processing this information to determine an estimate of thedistance. Rather, the receive-only interrogator may provide thisinformation to the master interrogator 1402 for further processing, andthe master interrogator 1402 may complete processing of this informationto derive an estimate of the distance between the receive-onlyinterrogator and the target device. To this end, master interrogator1402 may include circuitry (e.g., a processor, an ADC, etc.) forperforming such processing. For example, in some embodiments, areceive-only interrogator may generate a mixed RF signal indicative ofthe distance between the interrogator and the target device by mixingthe RF signal received from a target device with a local version of theRF signal transmitted by the master interrogator, that has beentransformed in a manner analogous to the processing performed by thetarget device (e.g., by passing the local version of the RF signalthrough a frequency multiplier), and may provide the mixed RF signal tothe master interrogator for further processing. Alternatively, thereceive only-interrogator may sample the mixed RF signal and provide rawADC counts to the master interrogator.

It should be appreciated that although, in some embodiments, each of thereceive-only interrogators 1404, 1406, and 1408 is configured to provideinformation to master interrogator 1402 via data lines 1414, in otherembodiments, each receive-only interrogator as well as the masterinterrogator may provide information indicative of the distance betweenthe receive interrogator and the target device to a separate processor(e.g., a processor not part of any interrogator device and, for example,on a separate semiconductor die) for further processing.

In some embodiments, during operation of system 1400, masterinterrogator 1402 may: (1) receive, via lines 1412, a fixed-frequencyreference signal; (2) generate, using the fixed-frequency referencesignal, an RF signal for transmission (e.g., an RF signal having a firstcenter frequency); and (3) transmit the generated RF signal to a targetdevice via the master interrogator's transmit antenna. The target devicemay receive the RF signal transmitted by the interrogator 1402,transform the received RF signal (e.g., by doubling its frequencies) toobtain a transformed RF signal having a second center frequency that isa harmonic of the first center frequency (e.g., twice the first centerfrequency), and transmit the transformed RF signal using a transmitantenna onboard the target device. Each of the interrogators 1402, 1404,1406, and 1406 may receive, via their respective receive antennas, aversion of the transformed RF signal.

After receiving the target device's responsive RF signal, interrogator1402 may use the responsive RF signal and a version of the transmittedRF signal to generate a first mixed RF signal indicative of a distancebetween the interrogator 1402 and the target device. Each ofreceive-only interrogators 1404, 1406, and 1408 may receive, via lines1412, a fixed-frequency reference signal and generate, using thereceived fixed-frequency reference signal, a local version of the RFsignal transmitted by master interrogator 1402. Next, each ofreceive-only interrogators 1404, 1406, and 1408 may receive a respectiveresponsive RF signal from the target device and may generate, using thereceived responsive RF signal and a respective local version of thetransmitted RF signal, a respective mixed RF signal indicative of adistance between the receive-only interrogator and the target device.

Next, in some embodiments, each of the interrogators 1402, 1404, 1406,and 1408 may: (1) determine an estimate of the distance between theinterrogator and the target device from the mixed RF signal; and (2)provide the determined estimate to the master interrogator 1402 or otherprocessor. In turn, the master interrogator 1402 or other processor mayestimate the location of the target device from the received distanceestimates. Alternatively, each of the interrogators 1404, 1406, and 1408may not be configured to determine an estimate of the distance, butinstead may provide information that can be used to make such adetermination (e.g., the mixed RF signals, a sampled version of themixed RF signals, etc.) to master interrogator 1402 or other processor.The master interrogator 1402 or other processor may then determine: (1)an estimate of the distance between each interrogator (both receive onlyand master interrogator) and the target device; and (2) determine thelocation of the target device based on these estimates.

FIG. 14C is a block diagram of a receive-only interrogator device 1404part of the illustrative localization system of FIG. 14A, in accordancewith some embodiments of the technology described herein. In someembodiments, receive-only interrogators 1406 and 1408 may also beimplemented in accordance with the illustrative embodiments ofreceive-only interrogator 1404 shown in FIG. 14C.

As described above, in some embodiments, receive-only interrogator 1404may be configured to operates phase coherently with master interrogator1402. For example, as shown in FIG. 14C, receive-only interrogator 1404may be configured to generate RF signals that are phase coherent withthe RF signals generated and transmitted by the master interrogator1402. To this end, receive-only interrogator 1404 includes waveformgeneration circuitry 1454 for generating frequency-modulated waveformsusing a phase locked loop in a “feedback loop perturbation” approach,which was described above with reference to FIG. 13B. However, unlikethe waveform generation circuitry 1320 shown in FIG. 13B, the waveformgeneration circuitry 1454 replaces the fixed-frequency referenceoscillator 1336 with shared fixed-frequency reference oscillator 1410(which is shared among all the receive-only interrogators 1404, 1406,and 1408 shown in FIG. 14A). As shown in FIG. 14C, the sharedfixed-frequency reference oscillator 1410 is coupled to frequencymultiplier 1328 via line 1412.

As shown in FIG. 14C, the waveform generator circuitry 1454 alsoincludes a voltage controlled oscillator (VCO) 1322, signal splitter1324, programmable digital divider 1326 that is programmable by inputprovided via line 1325, summation block 1330, loop filter 1332, and astep/impulse generator 1334. The summation block 1330 is within thephase locked loop so that a step and/or impulse generated bystep/impulse generator 1334 may be fed directly into the loop therebyperturbing the loop to sweep up to a desired frequency thencorrect-back-down to its programmed frequency. This perturbation in thefeedback loop would cause an up-then-down chirp, relying on a secondorder transfer function of the loop filter 1332 so that the outputprovided on line 1327 is a linear chirp.

The RF signals provided on line 1327 are processed, by interrogator1404, in a manner similar to RF signals provided via line 830 shown inFIG. 8B. As shown in FIG. 14C, the RF signals are provided, via line1327, to frequency multiplier circuitry 837, which increases thefrequencies in the RF signals by a desired factor. For example, in theillustrative embodiment of FIG. 14C, the frequency multiplier circuitry837 increases the frequencies in the RF signals by a factor of 16 (e.g.,from RF signals having a center frequency of 7.5 GHz to RF signalshaving a center frequency of 120 GHz). However, in other embodiments,the frequency multiplier circuitry 837 may increase the frequencies inthe RF signal by any other suitable factor (e.g., by a factor of 2, 4,8, 32, etc.), as aspects of the technology described herein are notlimited in this respect. The frequency multiplier circuitry 837 may beimplemented in any suitable way (e.g., using one frequency multiplier ora series of frequency multipliers with zero, one, or multipleamplification stages in the series).

The RF signals output by frequency multiplier circuitry 837 areamplified by amplifier 838 and mixed, using frequency mixer 840, with RFsignals received from a target device by receive antenna 116 andamplified by amplifier 842 to obtain mixed RF signals output fromfrequency mixer 840 on line 841. The mixed RF signals output on line 841may be indicative of the distance between interrogator device 825 andthe target device. The mixed signals output on line 841 may be furtherprocessed in any suitable way and, for example, may be processed by oneor more amplifiers and/or filters prior to being digitized using an ADC.

In some embodiments, the circuitry shown within block 1452 may beimplemented as integrated circuitry integrated with a semiconductor die.However, in other embodiments, one or more components within block 1452may be implemented not on a semi-conductor die (e.g., as a discretecomponent on a PCB) and/or one or more components not within block 1452may be implemented as integrated circuitry on a semiconductor die (e.g.,loop filter 1332).

It should be appreciated that the receive-only interrogator 1404 doesnot include either transmit circuitry or a transmit antenna. Asdiscussed above, this may reduce the cost of manufacturing, the size,and the power consumption of the receive-only interrogator relative toan interrogator device that performs both transmit and receivefunctions.

FIG. 14B is a block diagram of an illustrative localization system 1430comprising multiple synchronized (e.g., phase coherent) interrogatorsincluding master interrogator 1432 and three receive-only interrogators1434, 1436, 1438. Although there are three receive-only interrogatorsshown in the illustrative embodiment of FIG. 14B, in other embodiments,a localization system may include any suitable number (e.g., one, two,four, five, six, seven, eight, nine, ten, etc.) of receive-onlyinterrogators synchronized with master interrogator 1432. In addition,although in the illustrated embodiment of FIG. 14B each of theinterrogators 1434, 1436, and 1438 is a receive-only interrogator, inother embodiments, any of the interrogators 1434, 1436, and 1438 may becapable of transmitting and receiving RF signals, but may be configuredto operate in a receive-only mode.

The system 1430 further includes synchronization circuitry comprisingshared direct digital synthesizer 1440 and lines 1442 configured toprovide output of DDS 1440 to each of the interrogators 1432, 1434,1436, and 1438. The master interrogator 1432 may be of any suitable typeincluding any of the types interrogators described herein. Each ofinterrogators 1434, 1436, and 1438, may be of any suitable typeincluding the type described with reference to FIG. 14D.

In some embodiments, any one (e.g., all) of the receive-onlyinterrogators 1434, 1436, and 1436 may be configured to generateinformation indicative of the distance between the interrogator and thetarget device. A receive-only interrogator may provide the generatedinformation to the master interrogator 1432 via data lines 1444. Forexample, in some embodiments, each receive-only interrogator may beconfigured to determine an estimate of the distance between itself andthe target device and provide the determined estimate to masterinterrogator 1432. Based on the provided estimates, the masterinterrogator 1432 may determine a location of the target device and mayinclude circuitry (e.g., a processor) for performing such adetermination.

As another example, in some embodiments, a receive-only interrogator mayobtain information indicative of the distance between the receiveinterrogator and the target device, but may not be configured tocomplete processing this information to determine an estimate of thedistance. Rather, the receive-only interrogator may provide thisinformation to the master interrogator 1432 for further processing, andthe master interrogator 1432 may complete processing of this informationto derive an estimate of the distance between the receive-onlyinterrogator and the target device. To this end, master interrogator1432 may include circuitry (e.g., a processor, an ADC, etc.) forperforming such processing. For example, in some embodiments, areceive-only interrogator may generate a mixed RF signal indicative ofthe distance between the interrogator and the target device by mixingthe RF signal received from a target device with a local version of theRF signal transmitted by the master interrogator, that has beentransformed in a manner analogous to the processing performed by thetarget device (e.g., by passing the local version of the RF signalthrough a frequency multiplier), and may provide the mixed RF signal tothe master interrogator for further processing. Alternatively, thereceive only-interrogator may sample the mixed RF signal and provide rawADC counts to the master interrogator. In other embodiments, eachreceive-only interrogator as well as the master interrogator may provideinformation indicative of the distance between the receive interrogatorand the target device to a separate processor (e.g., a processor notpart of any interrogator device and, for example, on a separatesemiconductor die) for further processing.

In some embodiments, during operation of system 1430, masterinterrogator 1432 may: (1) receive, via lines 1442, a reference RFsignal synthesized by DDS 1440; (2) generate, using the reference RFsignal, an RF signal for transmission (e.g., an RF signal having a firstcenter frequency); and (3) transmit the generated RF signal to a targetdevice via the master interrogator's transmit antenna. The target devicemay receive the RF signal transmitted by the interrogator 1432,transform the received RF signal (e.g., by doubling its frequencies) toobtain a transformed RF signal having a second center frequency that isa harmonic of the first center frequency (e.g., twice the first centerfrequency), and transmit the transformed RF signal using a transmitantenna onboard the target device. Each of the interrogators 1432, 1434,1436, and 1436 may receive, via their respective receive antennas, aversion of the transformed RF signal.

After receiving the target device's responsive RF signal, interrogator1432 may use the responsive RF signal and a version of the transmittedRF signal to generate a first mixed RF signal indicative of the distancebetween the interrogator 1432 and the target device. Each ofreceive-only interrogators 1434, 1436, and 1438 may receive, via lines1442, the reference signal generated by the DDS 1440, and generate usingthe received reference signal, a local version of the RF signaltransmitted by master interrogator 1432. Next, each of receive-onlyinterrogators 1434, 1436, and 1438 may receive a respective responsiveRF signal from the target device and may generate, using the receivedresponsive RF signal and a respective local version of the transmittedRF signal, a respective mixed RF signal indicative of the distancebetween the receive-only interrogator and the target device.

Next, in some embodiments, each of the interrogators 1432, 1434, 1436,and 1438 may: (1) determine an estimate of the distance between theinterrogator and the target device from the mixed RF signal; and (2)provide the determined estimate to the master interrogator 1432 or otherprocessor. In turn, the master interrogator 1432 or other processor mayestimate the location of the target device from the received distanceestimates. Alternatively, each of the interrogators 1434, 1436, and 1438may not be configured to determine an estimate of the distance betweenthe interrogator and the target device, but instead may provideinformation that can be used to make such a determination (e.g., themixed RF signals, a sampled version of the mixed RF signals, etc.) tomaster interrogator 1432 or other processor. The master interrogator1432 or other processor may then determine: (1) an estimate of thedistance between each interrogator (both receive only and masterinterrogator) and the target device; and (2) determine the location ofthe target device based on these estimates.

FIG. 14D is a block diagram of a receive-only interrogator device 1434part of the illustrative localization system of FIG. 14B, in accordancewith some embodiments of the technology described herein. In someembodiments, receive-only interrogators 1436 and 1438 may also beimplemented in accordance with the illustrative embodiments ofreceive-only interrogator 1434 shown in FIG. 14D.

As described above, receive-only interrogator 1434 operates phasecoherently with master interrogator 1432. For example, as shown in FIG.14D, receive-only interrogator 1434 is configured to generate RF signalsthat are phase coherent with the RF signals generated and transmitted bythe master interrogator 1432. To this end, receive-only interrogator1434 includes waveform generation circuitry 1464 for generatingfrequency-modulated waveforms using a direct digital synthesizer in a“swept reference” approach, which was described above with reference toFIG. 13A. However, unlike the waveform generation circuitry 1300 shownin FIG. 13A, the waveform generation circuitry 1464 replaces the DDS1310 with shared direct digital synthesizer 1440 (which is shared amongall the receive-only interrogators 1434, 1436, and 1438 shown in FIG.14B). As shown in FIG. 14D, the shared DDS 1440 is coupled to frequencymultiplier 1308 via line 1442.

As shown in FIG. 14D, the waveform generator circuitry 1464 alsoincludes a voltage controlled oscillator (VCO) 1302, signal splitter1304, programmable digital divider 1306 that is programmable by inputprovided via line 1305, and loop filter 1312. The DDS 1440 operates as areference oscillator for the resulting phase locked loop. In someembodiments, the DDS 1440 may be a digital synthesizer that stores(e.g., in a memory part of DDS 1440) values for a digital waveform(e.g., a sinusoid, a chirp, or any other suitable waveform). The DDS1440 may be configured to “play back” the stored values through adigital to analog converter (DAC). That is, the DDS 1440 may beconfigured to process the stored values using a DAC, which may be partof the DDS 1440 in some embodiments, and output the resulting analogvalues. The rate at which the DDS 1440 outputs the stored values for thedigital waveform may determine its output frequency. In someembodiments, the DDS 1440 may be chirp-modulated above and below acenter reference clock frequency, thereby causing the output of the VCO1302 to chirp at its carrier frequency. The DDS 1310 may be chirpmodulated in any of a variety of ways, examples of which are providedherein. The output of DDS 1310 is multiplied-up in the PLL therebyproviding a chirp at the microwave frequency of interest at the RF Outline 1307.

The RF signals provided on line 1307 are processed, by interrogator1434, in a manner similar to RF signals provided via line 830 shown inFIG. 8B. As shown in FIG. 14D, the RF signals are provided, via line1307, to frequency multiplier circuitry 837, which increases thefrequencies in the RF signals by a desired factor (e.g., as discussedabove with reference to FIG. 14C). The RF signals output by frequencymultiplier circuitry 837 are amplified by amplifier 838 and mixed, usingfrequency mixer 840, with RF signals received from a target device byreceive antenna 116 and amplified by amplifier 842 to obtain mixed RFsignals output from frequency mixer 840 on line 841. The mixed RFsignals output on line 841 may be indicative of a distance betweeninterrogator device 825 and the target device. The mixed signals outputon line 841 may be further processed in any suitable way and, forexample, may be processed by one or more amplifiers and/or filters priorto being digitized using an ADC.

In some embodiments, the circuitry shown within block 1462 may beimplemented as integrated circuitry integrated with a semiconductor die.However, in other embodiments, one or more components within block 1462may be implemented not on a semi-conductor die (e.g., as a discretecomponent on a PCB) and/or one or more components not within block 1462may be implemented as integrated circuitry on a semiconductor die (e.g.,loop filter 1312). It should be appreciated, like interrogator 1404, thereceive-only interrogator 1434 does not include either transmitcircuitry or a transmit antenna. As discussed above, this may reduce thecost of manufacturing, the size, and the power consumption of thereceive-only interrogator relative to an interrogator device thatperforms both transmit and receive functions.

FIG. 17 is a flowchart of an illustrative process 1700 for determiningthe location of a target device using multiple synchronized interrogatordevices including at least one master interrogator device and areceive-only interrogator device, in accordance with some embodiments ofthe technology described herein. In some embodiments, the receive-onlyinterrogator may not be capable of transmitting RF signals (e.g., it maynot have circuitry for generating RF signals for transmitting using atransmit antenna and/or a transmit antenna). In other embodiments, thereceive-only interrogator may be capable of transmitting and receivingRF signals (e.g., it may have a transmit RF antenna and circuitry forgenerating RF signals for transmission by the transmit antenna), but maybe configured to operate in a receive-only mode. Process 1700 may beperformed by any suitable system and, for example, may be performed bysystem 200 described with reference to FIG. 2, system 1400 describedwith reference to FIG. 14A, and system 1430 described with reference toFIG. 14B.

Process 1700 begins at act 1702, where RF synthesis information isgenerated by the system performing process 1700. For example, the RFsynthesis information may comprise a fixed-frequency reference signalgenerated by fixed-frequency reference oscillator (e.g., oscillator1410). As another example, the RF synthesis information may comprise areference signal generated by a direct digital synthesizer (e.g., DDS1440).

At act 1704, the master interrogator in the system performing process1700 generates a first RF signal using the RF signal synthesisinformation generated at act 1402. For example, master interrogator 1402may generate the first RF signal using the fixed-frequency referencesignal generated by oscillator 1410. As another example, masterinterrogator 1432 may generate the first RF signal using the referencesignal generated by DDS 1440. After the first RF signal is generated atact 1704, the master interrogator uses its transmit antenna to transmitthe first RF signal to a target device at act 1706.

At act 1708, the master interrogator may receive a second RF signal fromthe target device using the master interrogator's receive antenna (the“first” receive antenna). The received second RF signal is a result ofpropagation, from the target device to the master interrogator, of an RFsignal generated by the target device in response to receiving the firstRF signal from the master interrogator.

At act 1710, a receive-only interrogator part of the system executingprocess 1700 generates a third RF signal using the RF signal synthesisinformation generated at act 1402. For example, receive-onlyinterrogator 1404 may generate the third RF signal using thefixed-frequency reference signal generated by oscillator 1410. Asanother example, receive-only interrogator 1434 may generate the thirdRF signal using the reference signal generated by DDS 1440.

At act 1712, the receive-only interrogator may receive a fourth RFsignal from the target device using the receive-only interrogator'sreceive antenna (the “second” receive antenna). The received fourth RFsignal is a result of propagation, from the target device to the masterinterrogator, of an RF signal generated by the target device in responseto receiving the first RF signal from the master interrogator. Althoughthe second RF signal and the fourth RF signal may have the samefrequency content they need not and, in any case, they are received bydifferent devices, as the second RF signal is received by a masterinterrogator and the fourth RF signal is received by the receive-onlyinterrogator different from the master interrogator.

At act 1714, the master interrogator generates, using the first andsecond RF signals, a first mixed RF signal. The first mixed RF signalmay be indicative of a distance between the master interrogator and thetarget device. The first mixed RF signal may be generated in anysuitable way including in any of the ways described herein. For example,the master interrogator may generate the first RF mixed signal at leastin part by: (1) transforming the first RF signal in a manner analogousto how the target device transforms received RF signals prior toretransmitting them (e.g., using one or multiple frequency multipliers);and (2) mixing the transformed RF signal with the second RF signalreceived by the first receive antenna.

At act 1716, the receive-only interrogator generates, using the thirdand fourth RF signals, a second mixed RF signal. The second mixed RFsignal may be indicative of a distance between the receive-onlyinterrogator and the target device. The second mixed RF signal may begenerated in any suitable way including in any of the ways describedherein. For example, the receive-only interrogator may generate thefirst RF mixed signal at least in part by: (1) transforming the third RFsignal in a manner analogous to how the target device transformsreceived RF signals prior to retransmitting them (e.g., using one ormore frequency multipliers); and (2) mixing the transformed RF signalwith the fourth RF signal received by the second receive antenna.

At act 1720, the system performing process 1700 may determine thedistance between the master interrogator and the target device using thefirst mixed RF signal obtained at act 1714. This may be done in anysuitable way including in any of the ways described with reference toact 1506 of process 1500. For example, the first mixed RF signal may besampled using an ADC and a Fourier transform (e.g., a discrete Fouriertransform) may be applied to the samples to obtain a time-domainwaveform. The time-domain waveform may be processed to obtain anestimate of the time of flight between the interrogator and the targetdevice. The estimate of the time of flight may be converted (e.g., basedon the speed of propagation of RF signals through air) to an estimate ofthe distance between the interrogator and the target device. Thisprocessing may be performed by the master interrogator, by an externalprocessor external to the master interrogator, or by a combination ofthe master interrogator (e.g., the ADC may be onboard the masterinterrogator device) and an external processor (e.g., the Fourieranalysis).

At act 1722, the system performing process 1700 may determine thedistance between the receive-only interrogator and the target deviceusing the second mixed RF signal obtained at act 1716. This may be donein any suitable way including in any of the ways described above withreference to act 1720.

Finally, at act 1724, the system performing process 1700 may determine alocation of the target device using the distance between the masterinterrogator and the target device determined at act 1720 and thedistance between the receive-only interrogator and the target devicedetermined at act 1722. This may be done in any suitable way and, forexample, using least-squares techniques. The processing of act 1724 maybe performed by the master interrogator (in embodiments where the masterinterrogator contains a processor), by an external processor external tothe master interrogator, or any suitable combination thereof.

It should be appreciated that process 1700 is illustrative and thatthere are variations. For example, although in the illustrativeembodiment of FIG. 17, the location of the target device is estimatedfrom two distance measurements (a measurement of distance between themaster interrogator and the target device and a measurement of distancebetween a receive-only interrogator and the target device), in otherembodiments, more than two distance measurements may be used todetermine the location of the target device. For example, in someembodiments, each of multiple receive-only interrogators (e.g., each oftwo, three, or four receive-only interrogators) may be used to obtain arespective distance measurement to the target device such that, togetherwith the distance measurement obtained by the master interrogator, threeor more distance measurements may be used to determine the location ofthe target device.

Having thus described several aspects some embodiments, it is to beappreciated that various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be within the spirit andscope of the present disclosure. Accordingly, the foregoing descriptionand drawings are by way of example only.

The above-described embodiments of the present disclosure can beimplemented in any of numerous ways. For example, the embodiments may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers.

Also, the various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages and/or programming or scripting tools, and also may becompiled as executable machine language code or intermediate code thatis executed on a framework or virtual machine.

In this respect, the concepts disclosed herein may be embodied as anon-transitory computer-readable medium (or multiple computer-readablemedia) (e.g., a computer memory, one or more floppy discs, compactdiscs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other non-transitory, tangible computer storage medium)encoded with one or more programs that, when executed on one or morecomputers or other processors, perform methods that implement thevarious embodiments of the present disclosure discussed above. Thecomputer-readable medium or media can be transportable, such that theprogram or programs stored thereon can be loaded onto one or moredifferent computers or other processors to implement various aspects ofthe present disclosure as discussed above.

The terms “program” or “software” are used herein to refer to any typeof computer code or set of computer-executable instructions that can beemployed to program a computer or other processor to implement variousaspects of the present disclosure as discussed above. Additionally, itshould be appreciated that according to one aspect of this embodiment,one or more computer programs that when executed perform methods of thepresent disclosure need not reside on a single computer or processor,but may be distributed in a modular fashion amongst a number ofdifferent computers or processors to implement various aspects of thepresent disclosure.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. The functionality of the program modules may becombined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconveys relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Various features and aspects of the present disclosure may be usedalone, in any combination of two or more, or in a variety ofarrangements not specifically discussed in the embodiments described inthe foregoing and is therefore not limited in its application to thedetails and arrangement of components set forth in the foregoingdescription or illustrated in the drawings. For example, aspectsdescribed in one embodiment may be combined in any manner with aspectsdescribed in other embodiments.

Also, the concepts disclosed herein may be embodied as a method, ofwhich an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A device, comprising: a receive antennaconfigured to receive a first radio-frequency (RF) signal having a firstcenter frequency; a first transmit antenna configured to transmit asecond RF signal having a second center frequency that is a harmonic ofthe first center frequency; a second transmit antenna configured totransmit a third RF signal having a third center frequency that is aharmonic of the first center frequency and is different from the secondcenter frequency; first circuitry, coupled to the receive antenna and tothe first transmit antenna, configured to generate the second RF signalusing the first RF signal and provide the second RF signal to the firsttransmit antenna for transmission; and second circuitry, coupled to thereceive antenna and to the second transmit antenna, configured togenerate the third RF signal using the first RF signal and provide thethird RF signal to the second transmit antenna for transmission.
 2. Thedevice of claim 1, further comprising: a semiconductor die, wherein eachof the first circuitry and the second circuitry is integrated with thesemiconductor die.
 3. The device of claim 1, wherein the first circuitrycomprises a first frequency multiplier and the second circuitrycomprises a second frequency multiplier different from the firstfrequency multiplier.
 4. The device of claim 1, further comprising: athird transmit antenna configured to transmit a fourth RF signal havinga fourth center frequency that is a harmonic of the first centerfrequency and is different from each of the second center frequency andthird center frequency; and third circuitry, coupled to the receiveantenna and to the third transmit antenna, configured to generate thefourth RF signal using the first RF signal and provide the fourth RFsignal to the third transmit antenna for transmission.
 5. The device ofclaim 1, wherein the receive antenna is configured to receive microwaveRF signals, and wherein each of the first and second transmit antennasis configured to transmit microwave RF signals.
 6. A device, comprising:a transmit antenna configured to transmit, to a target device, a firstradio-frequency (RF) signal having a first center frequency; a firstreceive antenna configured to receive, from the target device, a secondRF signal having a second center frequency that is a harmonic of thefirst center frequency; a second receive antenna configured to receive,from the target device, a third RF signal having a third centerfrequency that is a harmonic of the first center frequency and isdifferent from the second center frequency; first circuitry configuredto obtain, using the first RF signal and the second RF signal, a firstmixed RF signal indicative of a first distance between the device andthe target device; and second circuitry configured to obtain, using thefirst RF signal and the third RF signal, a second mixed RF signalindicative of a second distance between the device and the targetdevice.
 7. The device of claim 6, further comprising: a semiconductordie, wherein each of the first circuitry and the second circuitry isintegrated with the semiconductor die.
 8. The device of claim 6, whereinthe first circuitry comprises a first frequency mixer and the secondcircuitry comprises a second frequency mixer different from the firstfrequency mixer.
 9. The device of claim 6, further comprising: a thirdreceive antenna configured to receive a fourth RF signal having a fourthcenter frequency that is a harmonic of the first center frequency and isdifferent from each of the second center frequency and third centerfrequency; and third circuitry, coupled to the transmit antenna and tothe third receive antenna, configured to generate, using the first RFsignal and the fourth RF signal, a third mixed RF signal indicative of athird distance between the device and the target device.
 10. The deviceof claim 6, wherein the transmit antenna is configured to transmitmicrowave RF signals, and each of the first and second receive antennasis configured to receive microwave RF signals.
 11. A device, comprising:a first receive antenna configured to receive a first radio-frequency(RF) signal having a first center frequency; a second receive antennaconfigured to receive a second RF signal having a second centerfrequency; a first transmit antenna configured to transmit a third RFsignal having a third center frequency different from each of the firstand second center frequencies; a second transmit antenna configured totransmit a fourth RF signal having a fourth center frequency differentfrom each of the first, second, and third center frequencies; andcircuitry comprising: a frequency mixer configured to generate a fifthRF signal by using the first RF signal and the second RF signal; firstcircuitry configured to generate the third RF signal using the fifth RFsignal; and second circuitry configured to generate the fourth RF signalusing the fifth RF signal.
 12. The device of claim 11, furthercomprising: a semiconductor die, wherein the circuitry is integratedwith the semiconductor die.
 13. The device of claim 11, wherein thefirst circuitry comprises a first frequency multiplier and the secondcircuitry comprises a second frequency multiplier different from thefirst frequency multiplier.
 14. The device of claim 11, furthercomprising: a third transmit antenna configured to transmit a sixth RFsignal having a sixth center frequency that is different from each ofthe third and fourth center frequencies, wherein the circuitry furthercomprises: third circuitry configured to generate the sixth RF signalusing the fifth RF signal.
 15. The device of claim 11, wherein each ofthe first and second receive antennas is configured to receive microwaveRF signals, and wherein each of the first and second transmit antennasis configured to transmit microwave RF signals.
 16. A device,comprising: a first transmit antenna configured to transmit, to a targetdevice, a first radio-frequency (RF) signal having a first centerfrequency; a second transmit antenna configured to transmit, to thetarget device, a second RF signal having a second center frequency; afirst receive antenna configured to receive, from the target device, athird RF signal having a third center frequency different from each ofthe first and second center frequencies; a second receive antennaconfigured to receive, from the target device, a fourth RF signal havinga fourth center frequency different from each of the first, second, andthird center frequencies; first circuitry configured to obtain, usingthe first RF signal, the second RF signal, and the third RF signal, afirst mixed RF signal indicative of a first distance between the deviceand the target device; and second circuitry configured to obtain, usingthe first RF signal, the second RF signal, and the fourth RF signal, asecond mixed RF signal indicative of a second distance between thedevice and the target device.
 17. The device of claim 16, furthercomprising: a semiconductor die, wherein each of the first circuitry andthe second circuitry is integrated with the semiconductor die.
 18. Thedevice of claim 16, wherein the first circuitry comprises a firstfrequency mixer and the second circuitry comprises a second frequencymixer different from the first frequency mixer.
 19. The device of claim16, further comprising: a third receive antenna configured to receive afifth RF signal having a fifth center frequency that is different fromeach of the third center frequency and fourth center frequency; andthird circuitry configured to generate, using the first RF signal, thesecond RF signal, and the fifth RF signal, a third mixed RF signalindicative of a third distance between the device and the target device.20. The device of claim 16, wherein each of the first and secondtransmit antennas is configured to transmit microwave RF signals, andeach of the first and second receive antennas is configured to receivemicrowave RF signals.